Abstract: An efficient method has been presented which is named secondary field finite element method for two-dimentional magnetotelluric numerical modeling. The two-dimentional electromagnetic differential equations of secondary field have been derived, and the equations of secondary field can be solved by finite element method when the boundary conditions are simple; it is easier to simulate topographic earth by taking subdivision to the rectangle mesh. We have calculated several models and compared with previous researcher’s results using total field method. The results obtained indicated that the algorithm provided in this paper was correct. And it can be confirmed that the topographic abnormalities both in TE mode and TM mode are obvious. The apparent resistivity of H-polarization is affected by terrain more easily than that of E-polarization. The shape of apparent resistivity is positive correlation with terrain in TE mode, but that is opposite in TM mode.

Key words: magnetotelluric, secondary field, topographic, finite element method