ObjectiveTo investigate the possible mechanism of Ruyi Heibai Power （如意黑白散， RHP） in the treatment of vitiligo. MethodsTwenty-four C57BL/6 mice were randomly divided into blank group， model group， high-dose and low-dose RHP groups， with 6 mice in each group. Model group， high- and low-dose RHP groups were all applied hydroquinone to establish vitiligo animal model. After modeling， High- and low-dose RHP groups were given 7.02 g/kg and 2.34 g/kg of RHP by gavage， respectively， while the blank group and model group were intragastrically given 10ml/kg of normal saline， once a day for 36 days. After administration， the skin lesions were observed with naked eye， and HE staining was used to observe the melanin content of the skin lesions. Immunohistochemistry was used to determine the expression of CD3⁺ and CD8⁺ T cells in skin tissue. Immunofluorescence staining was used to measure the expression of programmed death receptor 1 （PD-1） in the skin lesion tissue. RT-PCR was used to detect programmed cell death ligand 1 （PD-L1） mRNA expression. ELISA was used to detect serum superoxide dismutase （SOD）， tumor necrosis factor （TNF-α）， and tyrosinase （TYR） levels. ResultsCompared to those in the blank group， the skin of the mice in the model group was pale， and the melanin content was significantly reduced under the microscope after HE staining； the rate of excellent and good skin lesions decreased， and the melanin granules in the cells around the epidermis and hair follicles decreased significantly； the expression of CD3⁺ and CD8⁺ T cells in skin tissue increased significantly， and the expressions of PD-L1 mRNA and PD-1 decreased； the content of TYR decreased， while the content of SOD and TNF-α increased （P＜0.05）. Compared to those in the model group， the skin color of high- and low-dose RHP groups were deepened， and the melanin content increased； the rate of excellent and good skin lesions increased， as well as the melanin granules in the spinous cell layer， basal cells and hair follicles； the expression of CD3⁺ and CD8⁺ T cells in the skin lesions decreased， while PD-L1 mRNA and PD-1 expression increased； the content of TYR increased， while the content of SOD and TNF-α decreased （P＜0.05）. Compared to the low-dose RHP group， the high-dose group had a larger pigment recovery area in the modeling area， an increased rate of excellent and good skin lesions， an increase in spinous cell layer， basal cells， and hair follicle melanin granules， a decrease in CD3⁺ and CD8⁺ T cells expression， an increase in the expression of PD-L1 mRNA and PD-1， an elevated TYR content， and decreased SOD and TNF-α contents （P＜0.05）. ConclusionRHP can increase skin melanin content of vitiligo mice.The mechanism of action may be related to activating the PD-1/PD-L1 signaling pathway， and then reducing the destruction of melanocytes by T cell-mediated autoimmunity.