Numerical simulation of electromagnetic pluses regional propagation is an important link in the analysis of electromagnetic environment effect, faced with technical challenges such as huge spatial scale, multiple radiation sources and complex geomorphology. This paper demonstrates a massively parallel 3D full-wave electromagnetic field simulation program software JEMS-FDTD and its development progress. Based on the large-scale parallel FDTD method and adaptive mesh refinement technology, an efficient full-wave time-domain computation method for large-area electromagnetic pulse propagation is developed. The numerical simulation of regional propagation of electromagnetic pulse in 1000 square kilometers city has been realized. This work verifies the feasibility of the software in the simulation of electromagnetic pluses regional propagation.