Abstract: Based on mechanism kinematic time-dependent reliability theory, an analytical model of kinematic accuracy reliability for rack and pinion steering mechanisms is presented. In this paper, the motion error function of a steering mechanism, which includes structural error and random error, is proposed with dimension tolerance. The analytical equations for the mean value and the variance of the motion error are derived. The kinematic time-dependent reliability of the rack and pinion steering mechanism is obtained by using fist－passage method. At last, a numerical example is given.