Abstract: The integral response deformation method is a commonly used seismic response analysis method for underground structures. However, in the process of solving the equivalent input seismic loads, it is necessary to apply the free-wave-field inertial force to all soil elements surrounded by the soil-structure interface in a free field model. The implementation processes are relatively complicated. Based on the discrete finite element model, the equivalent seismic loads caused by the surrounding stress of underground structures can be obtained through a static analysis of a substructure model consisting of only one layer of soil elements. On that basis, a modified integral response deformation method based on the substructure of soil layer is proposed, namely the first improved method. Furthermore, it is revealed that the influence of the inertial force of the soil layer on the equivalent seismic loads can be ignored. Then the second improved method of the integral response deformation method for underground structures is proposed. This method avoids the calculation and application of the free-wave-field inertial force of soil layers, thus effectively simplifying the implementation process of the integral response deformation method. The comparative analysis with the traditional integral response deformation method verifies that the proposed methods have good calculation accuracy, thus can be applied to the seismic response analysis and seismic performance research of underground structures such as subway stations and underground tunnels.