This paper proposed a novel buckling restrained steel plate shear wall (simply referred to as XSPSW) composed of X-shaped restrainers, an infill steel plate, and boundary restrainers. The X-shaped restrainers are placed on both sides of the infill steel plate, and the infill steel plate is divided into a series of diagonally arranged square subplates with a small height-to-thickness ratio. The X-shaped restrainers can effectively restrain the shear bucking of the infill steel plate and improve the seismic energy dissipation capacity of the shear wall. A refined numerical analysis model of the unstiffened steel plate shear wall (USPSW) and XSPSW was established and the validity of the model was verified by experiment. Numerical analysis was conducted to investigate the force mechanism and hysteretic behavior of the XSPSW. The results demonstrate that the mechanical behavior of the XSPSW is controlled by the square subplate. Compared to the USPSW, the shear buckling capacity, peak load, and energy dissipation capacity of the XSPSW are higher by at least 17%, 5%, and 7%, respectively, and the constraint efficiency of the out-of-plane displacement is larger than 55%. With the decrease in the height-to-thickness ratio of the subplate, the improvements in the shear buckling capacity, peak load, and energy dissipation capacity are increased to 29%, 31%, and 20%, respectively. Moreover, the constraint efficiency of the out-of-plane displacement rises to 92%, and the hysteretic curve tends to be full. The influence of the height-to-thickness ratio of the infill steel plate on the bearing capacity and energy dissipation capacity of the XSPSW is less than 2.5% and 1.2%, respectively.