• Male or female subjects, aged greater or equal to 18 years old at screening;

• Subjects diagnosed as high-risk ET according to the World Health Organization (WHO) 2016 criteria：1) who is older than 60 years and JAK2V617F positive at screening, 2) or who previously suffered from disease-related thrombosis or hemorrhage;

• Subjects who have previously received HU for ET, and the time interval between the last HU dose and the first dose of the study drug should not be less than 7 days;

• Interferon treatment-naïve, and for those who have previously received interferon the the time interval between the last dose of interferon and randomization should not be less than 1 month;

• Patients with confirmed hydroxyurea resistance or intolerant, as at least one of the following criteria is met:

‣ Platelet count remain greater than 600×10\^9 /L after at least 3 months of HU treatment at a dose ≥2g/d (dose ≥2.5 g/d if subject weight \> 80 kg);

⁃ Platelet count greater than 400\*10\^9/L while white blood cell (WBC) count lower than 2.5\*10\^9/L, or platelet count greater than 400\*10\^9 /L while hemoglobin lower than 100 g/L at any dose of HU;

⁃ Presence of HU-related toxicities at any dose of HU: e.g. ulcers in legs, or any unacceptable skin mucosal manifestations or fever;

• Platelet counts \> 450\*10\^9/L at screening;

• Neutrophil count ≥1.0\*10\^9/L at screening;

• Haemoglobin ≥11 g/dL at screening for males and 10 g/dL for females at screening;

• There is no serious function damage in liver and kidney: total bilirubin ≤1.5 upper limit of normal (ULN), alanine aminotransferase≤2.0 ULN, aspartate aminotransferase≤2.0 ULN, prothrombin time is prolonged by less than 4 seconds, Creatinine clearance ≥50 mL/min (according to Cockcroft-Gault formula) at screening;

• Both male and female subjects must agree take an appropriate contraceptive method, including:

‣ Male subjects: must agree to use reliable contraception from inform consent until 6 months following the last dose of the study drug.

⁃ Female subjects: Must meet at least one of the following conditions:

• i) Women without childbearing potential; ii) Women of childbearing potential: no pregnant or breastfeed, negative in blood pregnancy test within 4 days prior to the first dosing, and must agree to use reliable contraception from inform consent until 6 months following the last dose of the study drug;

• Subjects understand the objective, characteristic, method and possible adverse reactions of the study, voluntarily participate in this study, and sign informed consent.