As compared to existing three stations time difference location method in two-dimension plane, the bistatic time difference location method can heighten measurement accuracy and avoid the time difference ambiguity introduced by high PRF signal. At the same time, it also has the characteristic that the time reference between two major base stations can be derangement and that looking for the building position of base station is more convenience. With the help of geometric similarity recurrence method, this paper derives the bistatic time difference ranging formula directly from path difference equation in more forthright and more religious way.