Mathematical models of hydraulic transmission and mechanical subsystem were built through studying the shifting process of hydraulic machinery stepless transmission. Simulation model of hydraulic machinery stepless transmission was established based on AMESim. Simulation model of hydraulic transmission was constructed in Matlab/Simulink, joint simulation was employed. From the analysis results, it is concluded that shifting process was influenced by the main parameters of hydraulic machinery stepless transmission. The research provides suggestions for better shifting qualities and making contol strategy.