In order to establish a more accurate dynamic launch calculation model of the electromagnetic rail launcher, the equivalent frequency was introduced according to the current diffusion equation to simulate the change of skinning depth during the armature launching process, so as to calculate the motion process of the armature equivalently by using the results of the static simulation of the armature. A parameter extraction method was proposed, in which the corresponding relationship between electrical parameters and frequency was extracted by finite element simulation, and then the corresponding equivalent frequency was obtained by calculating the skin depth of the current in the launch process by the micro-element method. The equivalent frequency was combined with the above finite element simulation-results to calculate the dynamic electrical parameters of the system.The method is used in the whole system simulation, and the error between simulation and experiment is within 1%, which proves the effectiveness of the method.