Abstract: The structure of Tan-Lu fault zone in the Jiangsu-Anhui boundary area is very complex. This segment can be divided into two parts by the Huaihe river and their tectonic active characteristics are very different. With an emphasis on the south part, the fault segment is investigated according its topography, fault section, trench excavation. The result shows that the fault has dislocated the the stratum of middle Pleistocene. Compared with the north part, the tectonic active of south part in Quaternary was clearly weak. The cutting action of faults in other direction may be one of the possible reasons for the weakening.