The main problems of steel plate shear walls in current studies can be grouped into two categories: the unexpected bulky column or column failure in fully connected steel plate shear walls (FCSPSWs), and the low shear capacity in steel plate shear walls attached to the beam only (BOSPSW). Therefore, a partially connected steel plate shear wall with vertical square tube stiffeners (PCSPSW‐VSTS) is proposed in this work. There are three contribution points. Firstly, flexural stiffness thresholds of beams for BOSPSW and PCSPSW‐VSTS are proposed to ensure the uniform partial tension fields in the infill plates. Secondly, theoretical models of tension field inclination angles in BOSPSW and PCSPSW‐VSTS are proposed. Comparison results using proposed theoretical models, experiments, and simulations indicate that the proposed equations for the inclination angle can accurately predict the direction of principal tension stress for BOSPSW and PCSPSW‐VSTS. Thirdly, the shear capacity theoretical model of PCSPSW‐VSTS is proposed, which agrees well with experimental and numerical results. Besides, parametric studies of PCSPSW‐VSTS are conducted to investigate energy dissipation behavior and the effect of various stiffeners, which show that the square tube stiffener is efficient and economical, and the behavior of PCSPSW‐VSTS is better than that of FCSPSW in terms of shear capacity and energy dissipation. The proposed theoretical models can be adopted to develop the performance‐based seismic design of BOSPSW and PCSPSW‐VSTS. The proposed theoretical models avoid the simulation, the experiment, and the complicated solution of governing equations, which are suitable for designing buildings with SPSW in high‐intensity areas.