The complexity of transient electromagnetic forward modeling is required to be higher in practical production. The traditional Finite-Different Time-Domain (FDTD) algorithm adopts the model file mode in modeling, and can only use a few parameters to build some simple rule models, which is difficult to build complex models. At the same time, due to the lack of visualization module, the calculation results can not be displayed quickly. In view of the above problems, this paper develops the problem type suitable for the finitely difference Time domain algorithm based on GID platform, realizes the formatted output of software pre-processing process and model information, and writes the interface between FDTD algorithm and GID, realizes model information reading, unit number conversion and emission source identification, thus completing forward calculation and post-processing file generation. A 3D forward modeling software of transient electromagnetic complex model is developed, which integrates pre-processing, forward calculation and post-processing. In this paper, the research and development design, implementation method and main functions of the module of the whole set of software are introduced in detail. The calculation accuracy of the software is simulated and verified by simulating the layered and three-dimensional vertical contact zone models. Finally, a complex terrain model containing a complex shape target is designed for modeling and analysis. It can realize three-dimensional forward modeling of complex transient electromagnetic models.