<p>This paper focuses on the design of an improved sliding mode control (SMC) for a novel water proportional valve-controlled cylinder system and structural optimization of the valve. The aim of this paper is to solve two persistent challenges in the coal mining industry. One is that the large flow two-position three-way (3/2) on/off directional valve currently used on the hydraulic powered roof support (HPRS) cannot adjust the flow continuously and smoothly, which results in pressure and flow shock. The other is that the on/off logic control used on the HPRS cannot achieve accurate position and posture control of the hydraulic cylinder. In this paper, a novel 3/2 high water-based proportional directional valve (PDV) is developed. A structural optimization method combining Response Surface Methodology and Genetic Algorithm (RSM-GA) method is designed. Simulation results demonstrate enhanced dynamic response characteristics with errors of only 2.2% and 5.7%. Based on the new PDV, an improved observer-based sliding mode control (OBSMC) is proposed. The stability of the closed-loop system is proved using the Lyapunov method. The new control strategy effectively eliminates the nonlinearities, uncertainties, and external disturbances inherent in the valve-controlled cylinder (VCC). The system state and the unknown input are estimated using a high-gain observer (HGO). The robustness against external disturbances is improved using a disturbance observer (DOB). Co-simulation results validate the excellent performance of OBSMC.</p>