A Multi-center, randomized, double-blinded, double-dummy, parallel-controlled clinical trial to determine the efficacy and safety of Tripterygium Glycosides and Acitretin in patients with moderate to severe psoriasis vulgaris

INTERVENTION: TG treatment group:Take TG tablet every 2 slices,3 times a day,the placebo of Acitretin Capsules 3 pills on the noon once a day;Acitretin treatment group:Take the placebo of TG tablet every 2 slices,3 times a day,Acitretin Capsules 3 pills on the noon once a day; CONDITION: severe psoriasis vulgaris PRIMARY OUTCOME: PASI75; SECONDARY OUTCOME: PASI90;PASI50; INCLUSION CRITERIA: 1. Males and females aged between 18 and 75 years of age; 2. Moderate to severe psoriasis vulgaris defined by the following criteria: PASI >7 at screening and baseline; 3. Provide written informed consent; 4. Willing and able to comply with all aspects of the protocol.