Inclusion Criteria:  Each participant must meet all of the following criteria:  Male or female, 18~85 years of age; Diagnosis of malignant solid tumor; Participants receiving combined targeted therapy (including but not limited to tyrosine kinase inhibitors, cyclin-dependent kinase inhibitors) with immunotherapy (including but not limited to PD-1 inhibitors and/or PD-L1 inhibitors and/or CTLA-4 inhibitors); Participants experienced grade III or above thrombocytopenia (PC ≤50×109/L) at least once within 48 h of the screening period; No oral platelet-enhancing drugs were given before enrollmen. ECGO performance status ≤2;  Blood test:  Hemoglobin (Hb) ≥ 9.0 g/dL; Absolute neutrophils count (ANC) ≥ 1,500/μL;  Liver and renal functions:  Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 3*ULN (Upper Limits of Normal); Serum bilirubin ≤ 1.5*ULN; Albumin ≥ 2.5 g/dL; Serum creatinine ≤ 1.5*ULN (CTCAE Grade Ⅰ) Participants able to oral medication; Expected survival time ≥12 weeks during screening period; Participants with negative urine or serum pregnancy test during screening period; fertile potential participants must agree to use contraception for the whole study period and 30 days after discontinuity of investigational product treatment (infertile potential was defined as the condition including hysterectomy and bilateral oophorectomy, bilateral salpingectomy, tubal ligation and postmenopausal); Participants in the trial is voluntary and must strictly abide by the protocol; Participants must sign the written informed consent form.  Exclusion Criteria:  Participants meeting any of the following criteria will be excluded from the study:  Participants has any history of active congestive heart failure [New York Heart Association (NYHA) Grade III-IV], symptomatic ischemia, uncontrolled arrhythmia, pericardial disease, or myocardial infarction during the first 4 months of enrollment; Participants finished major operation within less than 28 days and for minor operation within less than 3 days; Participants had clinically significant acute or active bleeding (e.g., gastrointestinal or central nervous system) within 7 days prior to screening; Participants has medical-known hereditary prethrombotic syndrome (such as factor V Leiden mutation, prothrombin G20210A mutation or hereditary antithrombin III deficiency); Participants has a history of arterial or venous thrombosis within 3 months prior to screening; Participants had treatment with heparin and warfarin within 7 days prior to screening; Participants has history of chronic thrombocytopenia or hemorrhagic disease, or thrombocytopenia induced by other reasons besides targeted therapy and immunotherapy combination treatment(e.g., chronic liver disease or immune thrombocytopenic purpura); Participants had the treatment of platelet transfusion within 3 days before enrollment; Participants had administration of platelet growth factor (e.g., rhTPO, rhIL-11, Eltrombopag, or Romiplostim) for the treatment of thrombocytopenia induced by targeted therapy and immunotherapy combination treatment within 2 weeks prior to screening; Participants' thrombocytopenia responded effectively to hormone therapy; Participants are allergic to Avatrombopag or any of its excipients; Participants were in any other clinical trial of investigational product or device within 30 days prior to screening, except for observational study; Participants have any known concomitant history that may impair the safe completion of the study as assessed by the investigator, such as unstable angina, renal failure due to hemodialysis, or active infection requiring intravenous antibiotics; Participants are pregnant or lactating at the time of screening (as demonstrated by a positive serum β-HCG test) or baseline visit (positive urine β-HCG test)