The investigators are undertaking a parallel group, randomised controlled trial of 80 primary ITP adult patients from Qilu Hospital of Shandong University in China. One part of the participants are randomly selected to receive All-Trans Retinoic Acid(10mg tablet by mouth every 8 hours a day for 12 consecutive weeks, combining with dexamethasone (given orally at a dose of 40 mg per day for 4 days, the others are selected to receive high-dose of dexamethasone treatment (given orally at a dose of 40 mg daily for 4 days). Patients were monitored every 1 to 3 days at the first two weeks and every 1 to 4 weeks afterwards for platelet counts, and were monitored every 1 month for transaminitis and other side effects