Skillful motor control of human is achieved by the appropriate motor commands generating from the central nerve system. Internal model in the cerebellum may have great contribution for realizing accurate motor control. In this paper, the model for human motor control on manual tracking to moving visual target was constructed based on the experimental data of the visual tracking test for three groups ; normal healthy adults, patients with cerebellar ataxia and patients with Parkinson disease. Relationship between the model parameters and movement disorders were investigated. Furthermore, the compensation method for improving the motor function of patients were also considered.