Abstract: In underactuated systems, such as those represented by the steel water transportation process, system parameter uncertainties and external disturbances significantly affect the stability and safety of the system. Therefore, we propose a composite control strategy based on input shaping and particle swarm optimization (PSO) sliding mode control, aimed at effectively suppressing liquid sloshing and enhancing system robustness. Firstly, we model the liquid sloshing phenomenon as a pendulum system, and derive its equivalent dynamic model to provide a theoretical basis for accurately characterizing the sloshing behavior. Secondly, we design an input shaper is designed to optimize the control input signals, reducing transient oscillations and thereby improving transient performance. Based on this, we introduce sliding mode control, and design a robust controller to enhance the system's ability to cope with nonlinear characteristics, model uncertainties, and external disturbances. To further enhance the controller's performance, we apply the particle swarm optimization (PSO) algorithm to fine-tune the controller parameters, ensuring the system's stability and control accuracy under varying operational conditions. through simulation comparisons with traditional PID control and super-helical sliding mode control, the input shaping PSO sliding mode control achieves rapid stabilization of the system, improving the settling time by approximately 35%, from 20 s with PID control to 1.3 s, and reducing the maximum oscillation amplitude from 0.083 m in PID control to 0.024 m, which is a significant improvement compared to the 0.072 m of super-helical sliding mode control. This validates that the proposed composite control strategy offers a remarkable advantage in suppressing oscillations and enhancing the system's stability.