The purpose of this study is to evaluate whether etanercept combined with methotrexate are superiority than etanercept as monotherapy in the treatment of chinese severe plaque psoriasis. A phase IV, multicenter, randomized, double-blind, controlled trial was conducted.The primary outcome was Change from baseline in plaque psoriasis as assessed by PASI (psoriasis area and severity index) response or PASI75 (a patient that has an improvement from baseline PASI of at least 75%)