Abstract: According to the geometrical meaning of the kinematics accuracy reliability index, a method for kinematical accuracy reliability of main drive mechanism of diesel engine was presented by means of the combination of the improved PSO which has a lot of advantages such as less parameters, swift convergence rate and higher precision. The proposed method avoided the complicated partial derivatives in traditional method, and the computation was effectively reduced. It was shown by instances that the method was simple, practical and satisfied the requirements of calculated precision, thus a new valid method was provided for the solution of kinematical accuracy reliability of mechanism.