The motion output accuracy of the mechanism has been significantly affected by the performance degradation of components. In this paper, the cumulative factor of wear degradation is considered. On the premise of small samples, an analysis method of time?varying reliability of mechanisms is proposed. This analysis method applies the cosimulation of ADAMS and MATLAB. Based on the Archard wear model, the pin radius degradation is calculated and considered as a time series problem. The mechanism function is established according to the RSM method, and the ARIMA method is used to predict the change of the mechanism response value under the subsequent wear cycle to expand the data samples. Based on the interference model of stress?strength,the limit state equation of mechanism is established and the time?varying reliability is calculated. The convenience and accuracy of this method are demonstrated with a crank?slider mechanism.