In order to broaden the frequency variation range of nonlinear energy sink (NES), based on the principle of negative stiffness, a negative stiffness system is constructed by pre-compression springs, and a horizontal negative stiffness NES shock absorber is designed. Numerical simulation of negative stiffness NES shock absorber using ABAQUS finite element software to analyze the effects of length-width ratio of spring stroke, pre-compression, stiffness and damping ratio on the seismic performance of negative stiffness NES shock absorber in the state of no friction on the guide rod and no lateral buckling of the spring. The results show that increasing the pre-compression of the spring can improve the seismic performance of the shock absorber under the condition of fixed length-width ratio of spring stroke; under the condition of fixed spring pre-compression, as the length-width ratio of spring stroke increases, the bearing capacity of the shock absorber gradually decreases, and the seismic performance decreases. The increase in spring rate and damping ratio can significantly increase the bearing capacity of the shock absorber and improve the seismic performance. The research results provide a reference for the engineering application of negative stiffness NES.