An analysis method for the tolerance problem of the mechanism of remote center of motion used in surgical robot was conducted，which incorporated the identification and definition of the mechanical tolerance. An error propagation model was established using the direct linearization method. Besides, the absolute accuracy and repeat accuracy of the mechanism were analyzed using the probabilistic method and the deterministic method. In addition，sensitivity analysis of each error factor was conducted. The result shows that the mechanism can achieve a relatively high accuracy when using the IT6 standard designing level，and sensitivity analysis can find out the key factor that affects the mechanism accuracy.