Abstract: Owing to the capacity formula of two tangent conductor spheres being expressed by the series,the basic capacity formula of two tangent conductor spheres is restudied by using the method of mirror image for studying its concise expression result.A concise capacity formula is gained by applying the method of ＂balance zoom＂,the approximate formula is contrast with the accurate formula on three kinds of error according to the application of MATLAB software.The approximate formula is provided with high precision,it can become a common formula to use,the approximate formula has good function in general case.

Key words: mirror image, tangent conductor spheres, balance zoom method, concise capacity formula, compare error