Objective To observe the effects of different doses of protease inhibitor I (PSI) on behavior and the expression of tyrosine hydroxylase ( TH) and α-synuclein in the substantia nigra of rats, and to explore the optimal conditions for establishing a chronic Parkinson’s disease (PD) rat model induced by PSI. Methods Thirty SPF male rats were randomly and equally divided into three groups. Model groups were subcutaneously injected with PSI at a dose of 3 or 6 mg / kg, while the control group was injected with dimethyl sulfoxide solution at a dose of 3 mg / kg. After injection every other day (every Monday, Wednesday and Friday) for 2 weeks, the behavioral changes of PD rats were observed, and the changes of cells in the substantia nigra of the midbrain were observed by routine HE staining. The expression of TH and α- syn in the substantia nigra of dopaminergic neurons was determined by western blotting and immunohistochemical staining. Results Compared with that in the control group, the motor ability of the rats in the PSI model group was significantly decreased, the behavioral score in the pole climbing test was lower in the 3 mg / kg dose group than that in the 6 mg / kg dose group, and the behavioral score in the suspension test was higher in the 3 mg / kg dose group than that in the 6 mg / kg dose group. The result of HE staining showed that the substantia nigra cells of the model group were degenerated. The result of Western blot and immunohistochemistry showed that the expression of TH decreased significantly and that of α-syn increased significantly in the substantia nigra of rats. Conclusions The PSI rat model can replicate the behavioral and central and peripheral neurodegenerative changes of PD, making it an effective model to study the pathogenesis of PD.