Abstract: To study the velocity skin effect of railgun with solid armature, the relationships between the electromagnetic parameters and armature moving velocity were presented by Maxwell electromagnetic theory. The two-dimensional partial differential equations for electromagnetic field and temperature field in Cartesian coordinate system were set up; For a rectangular solid armature, the boundary conditions and excitation functions were described for the equations, the partial differential equations were resolved using finite difference method, the results were analyzed and the distributions of magnetic induction, temperature and current density within the rail and armature were obtained. The final results show that, the armature movement causes a high current density concentrating on the tail end