A mathematical calculation model of armature inductance gradient under the conditions of uniform and non-uniform magnetic field distribution between guide rails was deduced. The velocity frequency was introduced to simulate the velocity skin effect of armature emission process, and the time-harmonic simulation analysis was carried out on the 2D and the 3D electromagnetic field model. The inductance coefficient and the inductance gradient obtained from the simulation were used to calculate the dynamic inductance and the dynamic armature force in the simulation system. Electrical simulation and experiment results show that both the current and the velocity error are less than 2%, which proves the correctness and accuracy of dynamic inductance gradient analysis and parameter extraction method.