In an early clinical research, 138 patients completed the treatment of Psoriasis Vulgaris by Acitretin Capsules in 8 weeks, the results indicate 75 cases effectively (54.3%), 50 cases invalid(36.2%), 13 cases serious(9.4%). To investigate the influence of genetic factors on the curative effect and find the relationships between genetic variants and the response of Acitretin Capsules to treatment of Psoriasis Vulgaris.