Objective:To study the therapeutic mechanisms of “Xiegan Liangxue Jiedu Decoction” in the treatment of psoriasis. MethodsThe guinea pigs were randomly divided into the control group, model group, “Xiegan Liangxue Jiedu Decoction” group(herb group) and acitretin group. Popranolol emulsion was applied on ears back of guinea pigs to induce the psoriasis-like lesions. Each group was given corresponding treatment for 4 weeks. The general situation of guinea pigs, pathological changes of skin lesions, and the TNF-α expressions in the local skin and blood were observed.  Results:①The ear skin of the guinea pigs in the model group showed typical psoriatic lesions, which were obviously alleviated in herb group and acitretin group; ②Compared with the control group, the levels of TNF-α in the blood and local lesions were increased in the model group(P<0.05); compared with the model group, the levels of TNF-α in the blood and local lesions were decreased in the herb and acitretin groups(P<0.05); while there was no significant difference in the level of TNF-α between the herb and acitretin groups(P>0.05).  Conclusion:“Xiegan Liangxue Jiedu Decoction” acts to treat psoriasis by reducing TNF-α in the blood and local lesions.