Based on the large spring/stiffness method (LSM), this paper develops an improved technique (I-LSM) applicable to structural dynamic analysis with the assumption of Rayleigh damping. To estimate the accuracy of the technique, the dynamic response is analyzed for a 2-DOFs model respectively subjected to uniform/nonuniform seismic excitations. It indicates that the traditional LSM is inapplicable when Rayleigh damping is adopted. And the errors increase monotonously with the aggrandizement of damping. It’s also validated that the I-LSM based on the modification of displacement considering the influences of Rayleigh damping presented in this paper is able to effectively yield results almost identical to those of theoretical methods with errors beneath 4%.