This was an open-label, multi-center, randomized phase 2 study. This is a two-stage design.In the first stage, two dose groups were set up, the 100 mg bid dose group and the 200 mg qd dose group, which were randomized at 1:1, with 50 subjects in each group, and a total of 100 cases in the two groups. In the second stage, approximately 36 subjects were added to the randomized group.

According to the results of the interim analysis of the ZGJAK002 of Jaktinib, a comprehensive evaluation of the benefits and risks of subjects in the 100mg bid and 200mg qd groups, the investigator and the sponsor decided to expand the enrollment of approximately 36 subjects taking 100mg bid.

Inclusion criteria:

1、18 years age or older ,male or female;

2、Patients diagnosed with Primary Myelofibrosis according to WHO standard (2016 version), or patients diagnosed with Post-Polycythemia Vera Myelofibrosis or Post-Essential Thrombocythemia Myelofibrosis according to International Working Group Myeloproliferative Neoplasms Research and Treatment(IWG-MRT) standard. Both Janus Kinase 2(JAK2)mutation and JAK2 wild can be enrolled；

3、According to Dynamic International Prognostic Scoring System plus(DIPSS-plus) risk grouping criteria, patients with medium-risk-2 or high-risk myelofibrosis were assessed,Patients with grade 1 medium-risk myelofibrosis with hepatosplenomegaly and no response to existing treatment and requiring treatment can also be enrolled;

4、Subjects did not have a recent stem cell transplant program;

5、a life expectancy > 24 weeks;

6、Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2；

7、Splenomegaly: palpation of the splenic margin to or above the subcostal at least 5 cm；

8、Peripheral blood protocells ≤10%；

9、Patients who have not previously been treated with JAK inhibitors；

10、Absolute neutrophil count（ANC） ≥1000/uL, platelet count ≥75 × 109/L without growth factor, platelet production factor or platelet infusion.Subjects did not receive growth factor infusion within 2 weeks before randomization;

11、Seven days before randomization, the main organs were functioning normally, which met the following criteria： alanine transaminase（ALT）and aspartate aminotransferase（AST）≤2.5×upper limit of normal (ULN)； direct bilirubin（DBIL）and total bilirubin (TBIL)≤1.5×upper limit of normal (ULN）；serum creatinine ≤2.5×upper limit of normal (ULN)，calculated creatinine clearance（CrCl）≥50mL/min；

12、 Voluntarily sign informed consent in accordance with the requirements of the ethics committee;

13、Ability to follow study and follow-up procedures；

Exclusion Criteria:

1. Any significant clinical or laboratory abnormalities that the investigator considers to affect safety assessment, such as: a. uncontrolled diabetes (> 250 mg/dL, or 13.9 mmol > / L), b. had high blood pressure and antihypertensive drug treatment under two or unable to descend to the ranges (systolic blood pressure < 160 mmHg, diastolic pressure < 100 mmHg), c. peripheral neuropathy (NCI - CTC AE v4.03 standard grade 2 or above), d. thyroid dysfunction (> NCI - CTC AE v4.03 standard grade 2 or above);
2. The patients had a history of congestive heart failure, uncontrollable or unstable angina or myocardial infarction, cerebrovascular accident or pulmonary embolism in the first 6 months;
3. Screening of patients who have not fully recovered from surgery within the first 4 weeks;
4. Screening for patients with arrhythmia requiring treatment or QTc interval (QTcB) >480ms;
5. Screening for bacterial, viral, parasitic or fungal infections with any clinical symptoms that require treatment;
6. Patients with a history of congenital or acquired hemorrhagic diseases;
7. Patients who had previously undergone splenectomy or who had received radiotherapy of the splenic region within the first 12 months of screening;
8. Screening for HIV positive, active hepatitis b virus positive (HBsAg positive, hbv- dna positive or greater than 1000 copies /ml), anti-hcv antibody or hcv-rna positive;
9. Patients suffering from epilepsy or using psychotropic or sedative drugs at the time of screening;
10. Women who are planning to become pregnant or who are pregnant or breast- feeding, as well as those who were unable to use effective contraceptives throughout the trial;Male patients who do not use condoms during the administration and within 2 days (approximately 5 half-lives) after the last administration;
11. Patients who have suffered from malignant tumors (except cured basal cell carcinoma of the skin and carcinoma in situ of the cervix) in the past 5 years;
12. Combined with other serious diseases, the researchers believe that patients' safety or compliance may be affected;
13. Suspected allergic to Jakatinib hydrochloride or similar drugs;
14. Patients who have participated in the clinical trials of other new drugs or medical devices within the first 3 months;
15. Patients who were treated with any MF drug (e.g., hydroxyl urea), any immunomulator (e.g., thalidomide), any immunosuppressant, prednisone at or above 10mg/ day or equivalent bioactive level of glucocorticoid, growth factor (e.g.,erythropoietin ), or who were within 6 half-lives of the drug within 2 weeks prior to randomization;

No plan to share date of the trial