moving loads pass through the rough surface of beam. Considering the characteristics of random excitation, present nonlinear model of moving loads different beam roughness. The critical condition in of mean square is obtained by random Melnikov process. The response of structure under the combin of random and periodic excitation is simulated, and used to the variation of dynamic behaviors. It is concluded that speed, nonlinear dynamic behaviors midspan of beam are severely influenced by the random excitation. Therefore poor flatness of surface would increase the probability of occurrence of chaos.