The sound wave equation simulation method has been traditionally used in forward simulation of GPR. Nevertheless, as the radar wave is a kind of electromagnetic wave and the spread of the wave accords with Maxwell equation, the result of simulation is not precise enough. To solve this problem, the authors adopted the finite difference time domain method to perform simulation on the basis of Maxwell equation. In addition, the migration processing was conducted for the simulation result. It is found out that this method is correct and feasible.