Inclusion Criteria:  1.18 to 75 years of age 2.Moderate to severe chronic psoriasis, BSA≥3% 3.Duration of psoriasis≥6 months 4.Patients must be candidate for systemic therapy or phototherapy 5.No contradiction to Etanercept 6.Informed consent must be obtained 7.For female, ß-hCG test is negative and contraception is accepted  Exclusion Criteria:  Diagnosis of pustular psoriasis, erythroderma psoriasis or drug-induced psoriasis Having severe infections, including hepatitis, HIV and tuberculosis No live vaccines 12 weeks before enrollment, through the study and 1 year after the last dose of Etanercept Having significant allergies to biological agents Having the previous experience of biologics Having a history of malignancy Having contradictions to Etanercept Refusal of contraception Having serious or unstable/uncontrolled illnesses