Inclusion Criteria:  Between the age of 18 to 70, male or female; Diagnosed having SCLC via either histology or cytology; Extensive small-cell lung cancer with recurrence or progression within ≤6 months from the end of first-line therapy; At least one measurable lesion (non-intracranial, non-measurable after radiotherapy) according to RECIST version 1.1;. ECOG-PS score is 0-1; Expected survival time ≥12 weeks; Have faverable organ and hematopoietic function, with no serious abnormality of heart, lung, liver or kidney function or immune deficiency according to laboratory tests: Fertile male subjects and female subjects of reproductive age who are willing to take effective non-drug contraceptive measures from signing the informed consent form until 6 months after the last administration of the study drug. Blood pregnancy test results of women of childbearing age must be negative within 7 days before the first trial drug administration. Voluntarily participate in the clinical study and sign the informed consent  Exclusion Criteria:  Have a previous history of allergy, or are known to be severely allergic to either JK1201I or its excipients; Previous treatment with topoisomerase I inhibitor (such as irinotecan, topotecan, etc.); At the first use of the drug in this study, other anti-tumor chemotherapy or immunotherapy was stopped for < 4 weeks; CYP3A4 strong inducer was used within 2 weeks before the first administration, or CYP3A4 suppressor or UGT1A1 suppressor was used within 1 week; Patients with clinically serious gastrointestinal dysfunction (positive fecal ocidiocytic blood and severe gastrointestinal bleeding, gastrointestinal infection, obstruction or grade 1 or above diarrhea (increase of stool number ≥4 times per day)); Complicated with symptomatic brain metastasis, meningeal metastasis, spinal tumor invasion, spinal cord compression; Superior vena cava syndrome, obstructive atelectasis, and bone metastasis with local symptoms that may require non-medical treatment such as radiotherapy/surgery/endoscopic therapy/interventional therapy; For patients with brain metastasis (the distance from the end of whole brain radiotherapy to the first dose ≤7 days, and the distance from the end of SBRT radiotherapy to the first dose ≤3 days); Patients with severe heart disease within 6 months prior to enrollment, such as unstable angina, heart failure (New York Heart Association Heart function classification > Class II), coronary angioplasty or stenting, deep vein thrombosis, myocardial infarction, etc.; Or other diseases that may affect the subject's safety, such as deep vein thrombosis, stroke, stroke (except caval infarction), poorly controlled active bleeding or known bleeding constitution, etc.); Had a serious pulmonary disease, such as pulmonary fibrosis, active pulmonary tuberculosis, pulmonary hypertension, etc., within 6 months prior to inclusion; Other malignant tumors occurred within 5 years before enrollment, except carcinoma in situ of the cervix, squamous cell carcinoma of the skin or basal cell carcinoma which had been treated for radical treatment before; UGT1A1 suppressor (azanavir, giferozil, etc.) was used or had been used in combination drugs or within 7 days prior to the treatment of the study drugs; large amounts of pleural effusion and ascites needed to be treated (continuous pleural and abdominal effusion > 1000ml within 1 week); Toxicity of previous anti-tumor therapy (including chemotherapy/radiotherapy, surgical therapy, targeted therapy, immunotherapy, Chinese herbal therapy, endocrine therapy or other anti-tumor therapy) has not recovered (grade 1 or above as assessed by CTCAE version 5.0, Except for hair loss, alkaline phosphatase, glutamyltranspeptidase (GGT), or subjects eligible for inclusion after discussion with the investigator and sponsor); Subjects with severe infection within 4 weeks before the first medication, including but not limited to those with infectious complications, bacteremia and severe pneumonia requiring hospitalization; Pregnant or breast-feeding women; Presence of human immunodeficiency virus (HIV) or active hepatitis b (HBsAg positive and HBV-DNA titer ≥1x103 copy number /mL or 200IU/ mL; Subjects who have participated in other clinical trials within 4 weeks prior to obtaining informed consent; Have a clear history of mental disorders; Subjects considered unsuitable for the study by the investigator for other reasons.