In order to realize the function of tractor cruise control system, the tractor acceleration was controlled precisely. Due to the non-linear, road slope and vehicle quality changes caused by longitudinal dynamic system tractor mounted implement, wind resistance and other external interference factors existing, the control system robustness become the focus of the controller design. The longitudinal dynamic model of the tractor was established by using modular mechanism modeling methods and combining with the experimental data, and this model was realized in Simulink, compared with the real vehicle platform, the validation of the model met the demand. According to the nonlinear characteristics of the tractor longitudinal power transmission system, the longitudinal dynamic model of the tractor was linearized by the inverse model method. Based on the linearized model, the frequency response characteristic data of each working point and the working condition of the lower control object were obtained. The transfer function of the lower level object was identified by the frequency response experiment and the least square method. According to the transfer function and the nonlinear characteristics of longitudinal acceleration response, a sliding mode variable structure controller was designed. Compared with the PID control, the simulation results showed that the controller can effectively improve the robust performance of the system to nonlinear characteristics and external disturbances.