The dynamic load on drive axle housing has great significance for analyzing the strength of drive axle housing and studying the reliability life of drive axle housing, and road roughness has an important impact on dynamic load of drive axle housing. In this paper, the drive axle housing of agricultural machinery is select as the research object. Firstly, the dynamic model of the drive axle housing is established, and the vibration equation is calculated by Laplace transform and Laplace inverse transform, and then the vibration load time history is given based on the discrete data of road roughness obtained by field experiment. At last, the rainflow counting method is used to generate the load spectrum. The study has a certain reference and application value for the optimization design of drive axle housing of agricultural machinery.