| As is known to all, time and accuracy in calculation are two important standards to estimate efficiency of forward modeling. However, the relationship between this two factors are incompatible presented by all sorts of main algorithms nowadays. Take finite element method for example, the method has a reliable accuracy convergence theory, whereas it need infinitesimal element and higher order shape function to ensure its accuracy. As a result, the number of nodes will be largely increased, which restrain computing time. Besides, models are built by inputting many model and grid parameters in most of forward modeling program. It's a method of time consuming, and in addition to this, it also has difficulty in building complex models which are similar to real geological structures. Topographic effect is a common and important factor which will distort the apparent resistivity curve in geological field work. There are few researches focus on how to eliminate the influence caused by complex terrain.According to the problems mentioned above, we proposed some solving measures and solutions in this paper by realizing 2.5-D direct current electric field forward modeling using boundary element method.First, we reduced the node number and cut down the computing time. The increase of the computational efficiency come from two parts. One is by using 2.5 dimension model instead of 3 dimension model by Fourier transform, the other one is by dividing element only on the model's boundary due to the features of the BEM. Second, We simplified the work of building model by developing the function of the class in C++ and realized the algorithm for model self-dividing by writing gridding algorithm in C++ language. At last, we realized 2.5 dimension direct current electric field forward modeling with complex terrain and removed topographic effect by terrain correction using ratio method. Modeling results are in line with field experience and of high value for reference.
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