Clearances in rudder transmission mechanism have important influence on flight stability, maneuverability and control accuracy of launch vehicle. This paper firstly classifies the clearances in launch vehicle rudder transmission mechanism into three types, including clearances within linkage fits, clearances within rocker fits, clearances within rudder shaft fits. A theoretical analysis method of the clearance influence based on kinematic analysis is then proposed. The dynamics models within three types of clearances are built and simulated by ADAMS. From the comparison and analysis of the simulation results from ADAMS, it shows that the influence of three types of clearances in rudder transmission mechanism can be accurately computed by using the theoretical analysis method. It is able to evaluate the influence of exceeding tolerance clearances in engineering.