Abstract: Dynamic analysis of multibody systems with probabilistic parameters was presented. Dynamic modeling of multibody systems was obtained by Lagrange's method. The probabilistic differential algebraic equations were transformed into pure probabilistic differential equations by generalized coordinate partitioning method. The Newmark step-by-step integration method was used to calculate the results. Using the method of random factor method, the numerical characteristics of the system response were derived, and the results were expressed in statistic view. As an illustrating example, dynamic modeling of a rotating bar and sliding block system considering the probabilistic of load, geometric and physical parameters was presented. Compared with the result of Monte-Carlo numerical simulation method, the accuracy and efficiency of the method are verified. The results illustrate that the probabilistic parameters affect the dynamic response of the multibody system and the dynamic modeling with probabilistic parameters can objectively reflect the dynamic behavior of the objective systems.