Inclusion Criteria:  The subjects volunteered to join the study and signed informed consent, with good compliance; Age: 18-75 years old (when signing the informed consent form); Eastern Cooperative oncology Group (ECoG) Performance Status (PS) score: 0-2; The expected survival time is more than 24 weeks; Primary Myelofibrosis (PMF) was diagnosed according to World Health Organization (WHO) standard (2016 Edition), or Post Polycythemia Vera(PV)-MF or Post Essential Thrombocythemia (ET)-MF was diagnosed according to International Working Group-Myeloproliferative Neoplasms Research and Treatment (IWG-MRT) standard; JAK2 mutation or not was included in the study; According to Dynamic International Prognostic Scoring System (DIPSS) prognosis grading criteria, the patients with myelofibrosis were assessed as medium risk (including medium risk-1, medium risk-2) or high risk; Splenomegaly: palpate the splenic margin at least 5cm below the ribs (the distance from the costal margin to the farthest point of splenic protrusion); Peripheral blood primordial cells ≤ 10%; If anti myelofibrosis therapy (except JAK inhibitor) is being received before screening, the drug must be stopped at least 4 weeks before the random date; No growth factor, colony stimulating factor, thrombopoietin or platelet transfusion was received within 2 weeks before the examination, and hemoglobin (Hgb) ≥ 80g / L, platelet count (PLT) ≥ 100 within 7 days before the random date × 10^9 / L and neutrophil absolute value (neut) ≥ 1.0 × 10^9/L; The main organs were functional 7 days before the random date, which was in accordance with the following criteria: Total Bilirubin (TBIL) was less than 2 times the upper limit of normal value (ULN); Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST) were less than 2.5 times of ULN; Serum creatinine (Cr) < 1.5 times of ULN or creatinine clearance rate (Ccr) ≥ 50ml/min; The blood coagulation function should be checked in accordance with: prothrombin time (PT), activated partial thromboplastin time (APTT), international standardized ratio (INR) < 1.5 × ULN (not anticoagulant treatment); Left ventricular ejection fraction (LVEF) evaluated by color Doppler ultrasonography ≥ 50%; Female subjects of childbearing age should agree to use contraceptive measures (such as intrauterine device, contraceptive or condom) during the study period and within 6 months after the end of the study; The serum pregnancy test was negative within 7 days before the date of randomization and must be non lactating subjects; Male subjects should agree to use contraception during the study period and within 6 months after the end of the study period.  Exclusion Criteria:  Those who have received allogeneic stem cell transplantation in the past, or autologous stem cell transplantation within 3 months before the random date, or recently planned stem cell transplantation; Patients who have received JAK inhibitors in the past; Those who had undergone splenectomy or received splenic radiotherapy within 6 months before the date of randomization (including internal and external radiotherapy); Other malignancies were present or present within 3 years before the date of randomization. The following two cases can be included: other malignant tumors treated by single operation have achieved 5-year disease-free survival (DFS) in a row; Cured cervical carcinoma in situ, non melanoma skin cancer and superficial bladder tumor [ta (non-invasive tumor), tis (carcinoma in situ) and T1 (tumor infiltrating basement membrane)]; Patients with multiple factors (such as inability to swallow, postoperative gastrointestinal resection, acute and chronic diarrhea, intestinal obstruction, etc.) affecting oral or absorption of drugs; Non hematological toxicity caused by previous treatment did not return to ≤ 1 (excluding alopecia); Patients who received major surgical treatment or had obvious traumatic injury within 4 weeks before the date of randomization; At present, there are congenital bleeding or coagulation diseases, or are using anticoagulant therapy; Arteriovenous thrombotic events occurred within 6 months before the random date, such as cerebrovascular accident (including transient ischemic attack, cerebral hemorrhage, cerebral infarction), deep venous thrombosis and pulmonary embolism; A history of psychotropic substance abuse or mental disorder; Active or uncontrolled severe infection (≥ Common Terminology Criteria for Adverse Events(CTCAE)2 infection); Hepatitis B Virus (HBV) DNA≥ULN； Hepatitis C antibody positive and Hepatitis C Virus (HCV) RNA ≥ ULN; Myocardial ischemia or myocardial infarction, arrhythmia, QT interval prolongation (corrected QT interval (QTc) ≥ 450 ms for male, QTc ≥ 470 ms for female) and congestive heart failure (NYHA classification) of grade 2 or above; Blood pressure control is not ideal (systolic blood pressure ≥ 150 mmHg or diastolic blood pressure ≥ 100 mmHg); Renal failure requires hemodialysis or peritoneal dialysis; Newly diagnosed pulmonary fibrosis or drug-related interstitial lung disease within 3 months before the date of randomization; History of immunodeficiency, including Human Immunodeficiency Virus (HIV) positive or other acquired or congenital immunodeficiency diseases, or organ transplantation; Patients with epilepsy and need treatment; Had received chemotherapy, radiotherapy or other anti-cancer therapy within 4 weeks before the date of randomization; Within 2 weeks before the date of randomization, he received Chinese patent medicines (including compound cantharis capsule, Kang'ai injection, kang'laite capsule / injection, Aidi injection, Brucea javanica oil injection / capsule, Xiaoaiping tablet / injection, cinobufagin capsule, etc.) with anti-tumor indications specified in nmpa approved drug instructions; Uncontrolled pleural effusion, pericardial effusion or ascites; Patients with central nervous system involvement; There was a history of live attenuated vaccine inoculation within 4 weeks before the date of randomization or live attenuated vaccine inoculation was planned during the study period;