High-load disturbances during rotary tillage can cause significant wheel slip on the electric-drive mobile platform in the distributed horticulture facility. It is often required to control the speed-slip rate for the longitudinal stability of the distributed horticultural facility. In this study, a cascaded controller of vehicle speed–slip rate was proposed using integral robust vehicle speed and sliding-mode slip rate control. Its effectiveness was validated using simulations and vehicle experiments. Firstly, a dynamic model was established for the coupled system between the distributed electric-drive horticultural platform and the rotary tiller. Tire-soil interaction and the resistance of rotary tillage were also considered to explicitly incorporate the wheel rotational dynamics and external disturbance torques. Soil adhesion also led to variable tillage resistance. Moreover, a coupled modeling framework was constructed to describe the nonlinear relationship between longitudinal tire force and slip ratio. The traction generation was accurately characterized under deformable soil conditions. The slip regulation and speed stabilization were coordinated under high-load environments. Subsequently, an outer-loop vehicle speed controller was designed to incorporate integral robust control. The steady-state errors were eliminated from the operational disturbances for the high-speed stability. The integral term was used to compensate for the persistent disturbance-induced bias. While the robust component was enhanced, the controller’s tolerance to parametric uncertainties and unmodeled dynamics. Integral action was combined with robustness enhancement. The outer-loop controller maintained accurate speed tracking, even when sudden load fluctuations occurred. Furthermore, an inner-loop slip rate controller was developed using sliding-mode control. The optimal slip rate was obtained from the inverse tire model to serve as the reference input for the rapid convergence and precise tracking of slip rate. Sliding-mode control was selected for its high robustness against disturbances and modeling uncertainties, thereby enabling the dynamic response and strong anti-interference. The optimal slip rate corresponded to the traction peak region of the tire–soil interaction curve. Traction efficiency was maximized to prevent excessive slip. The outer and inner loops were coordinated for the longitudinal stability of the platform under high disturbance. A control strategy was then integrated for anti-slip driving and speed regulation. Specifically, the inner loop was used to rapidly suppress the deviations of the slip ratio, while the outer loop was for the global speed regulation using a cascaded structure. A hierarchical architecture of traction control was constructed, suitable for the distributed electric-drive systems. Simulation results indicate that the cascaded controller achieved an average speed error of 0.10 km/h under sudden muddy conditions, which was reduced by 16.6% and 67.7%, compared with the switching and speed control, respectively. The speed recovery time was 0.11 s, which was reduced by 64.5% and 68.6%, respectively. There was an average speed error of 0.07 km/h under variable tillage depths, which was reduced by 40.0% and 52.0%, compared with switching control and speed control, respectively. Experimental results indicate that an average speed error of 0.44 km/h was found under acceleration, which was reduced by 4.3% and 8.3%, compared with the switching and speed control, respectively. The average slip ratio was 0.15, which was reduced by 11.7% and 16.6%, respectively. There was an average speed error of 0.20 km/h under deep tillage, which was reduced by 20.0% and 37.5%, respectively. The average slip ratio was 0.13, which was reduced by 23.5% and 31.6%, respectively. Therefore, the cascaded controller can be expected to effectively suppress the slip ratio during rotary tillage, thereby enhancing the speed control performance and operational stability.