Abstract: A finite difference formulation is developed for computing the frequency domain electromagnetic fields due to a magnetic source in the presence of two-dimensional conductivity structures. The main principle of this forward modeling method is to synthesize data for three dimensional signal source with a series of different wave numbers in geologic structure's strike direction (direction x in Cartesion coordinate system). By the Fourier transformation the problem is transformed into the x-wave number(k_x) and two coupled partial differential equations for Hx(k_x, y, z) and Ex(k_x, y, z) are obtained. These equations can be solved by finite difference method in y-z plane. In the paper, four typical models are used for 2.5D forward modeling. Then we demonstrate the Hz curves for two-anomaly bodies in different depth, two-lean-anomaly bodies and down fault anomaly. Numerical modeling results clearly show the magnetic anomaly of the anomalous characteristics. Finally, we simulated the inter well exploration methods and obtained some good results in Ey and Hz.