The investigators are undertaking a multicenter, randomized controlled trial of 200 primary ITP adult patients from 5 medical centers in China. One part of the participants are randomly selected to receive Thalidomide (given at a dose of 150mg for 15 consecutive days), combining with dexamethasone (given intravenously at a dose of 40 mg per day for 4 days, the others are selected to receive high-dose of dexamethasone treatment (given intravenously at a dose of 40 mg daily for 4 days).