Starting from the Maxwell equations, this article studied the boundary conditions of 3D MT. By using the weighted residual method, we derived the three-dimensional MT finite element equation. The three-dimensional vector finite element hexahedral meshing mode was introduced and the basis functions were selected. Then we derived the three-dimensional magnetotelluric vector finite element stiffness coefficient matrix and discrete format. A three-dimensional vector finite element magnetotelluric forward Matlab program was done. The apparent resistivity curve of the dimensional COMMEMI 3D-1 model matches the international standard test data, which proves the correctness of 3D magnetotelluric forward program. With the analysis of high and low resistivity anomalies, it shows that tensor impedance map can roughly determine the anomaly characteristics, which enriches the magnetotelluric response characteristics of expression.