It is well-known that the distortion potential is a complicated function of both the terrain angle and the electrode spacing. In this paper polynomes are used to approximate the function, so that the calculation involved becomes quite simple. Afast computer program has been developed for topographic correction in resistivity method (omitted in this paper). Comparing to the results of analytical solution, the mean relative error is less than±0.1%, which meets the needs of field work. By virtue of the simplicity of the formula, calculations can be easily accomplished with a calculator. As a result, it provides a simple and fast technique of topographic correction for prompt and in-situ calculation of large amount of electrical survey data.