Objective To study the topical application of Tuhuai decoction and its disassembled prescriptions on skin function of mice with epidermal hyperplasia, and to provide a theoretical basis for the treatment of psoriasis. Methods According to the Denda method, skin barrier function in mice was destructed with tape, to produce epidermal hyperplasia model. Tuhuai decoction and its disassembled prescriptions with different concentrations of water and alcohol extracts were external applied on the mice. Since the beginning of the treatment, loss of skin moisture of both sides the trunk was detected with Multi-functional instrument at every day before using the medicine. Results Tuhuai decoction had function of reducing the amount of water loss of skin. The disassembled prescriptions, such as Angelica group, safflower group, Danshen root group, and water and ethanol extracts of Prtmella group can reduce the amount of water loss of skin effect. Conclusion Water and ethanol extracts of Tuhuai decoction has the functions of reducing water loss of skin and resisting hyperplasia,suitable for treating psoriasis by external application, setting a foundation for clinical treatment of psoriasis.