Abstract: The paper presents a simple method for calculating fighter gun recoil force based on a finite element model of gun and cantile'ver spring support. The recoil force is defined as the internal force, which is a dynamic response due to firing impulse input, in structural members of the model. Modal analysis and dynamic recoil force response are carried out by using SAP5 programme,and the frequency spectrum of impulse and recoil force response are established by FFT method so as to examine the contributions of the modal components dominating the response. The recoil force cruves worked out in theory are very close to those in the experiments, and the metbod used in this paper can directly be applied to complex aircraft structure and gun. system recoil force analysis. . '