A simplified model of the buckling-restrained steel plate shear wall (BRSPSW) was developed to simulate the steel plate-restraining panel interaction behavior that considers the high-order buckling deformation of steel plates. Based on the analysis of the simplified model, a theoretical equation to determine the out-of-plane interaction force was developed. Additionally, a push-over test was conducted to determine the interaction force between the steel plate and restraining panels. The results were used to validate the theoretical and finite element (FE) analyses. Furthermore, the FE method was applied to analyze the steel plate-restraining panel interaction behavior, and the effect of the gap on the out-of-plane interaction force was investigated. The FE results show that the interaction force of a thinner steel plate is higher than that of a thicker plate. As the gap increases, the interaction force increases rapidly to the peak value and then reduces gradually. Finally, the theoretical and FE results were compared. It was found that the theoretical equation can be used to calculate the out-of-plane interaction forces of BRSPSWs.