The Huaiyuan—Chihe fault intersects with the southern section of the Tan- Lu(Tancheng—Lujiang) fault zone, and is located in the section where the activity of the Tan- Lu fault zone gradually weakens. In order to obtain reliable geological evidence of activity of the Huaiyuan—Chihe fault, geomorphologic survey, trench excavation and sample age testing were carried at the northeastern margin of Jiushan Mountain in Anhui. Our study shows that the linear landform of the northeastern margin of Jiushan Mountain is mainly due to activity of the Huaiyuan—Chihe fault. In the multiple profiles in our survey, the fault show consistent features. The fault strikes NW, dips to NE with a dip angle of ~70° and has normal faulting component. The vertical fault throw of the fault is larger in the old strata while becomes smaller in the new strata and disappeared in the Quaternary layer. It shows that the fault has multi- period activities and its activity gradually weakens since middle Pleistocene. Through analysis of trench profile across the fault and dating, the fault had displaced Middle Pleistocene strata, the overlying top strata of Middle Pleistocene and Late Pleistocene strata are not affected, indicating that the fault should be a Middle Pleistocene fault and has been inactive since the Late Pleistocene. The activity of the Huaiyuan—Chihe fault is related to the neotectonic environment in its surrounding area. The Tan- Lu fault zone is the largest seismogenic structure in this area and its activity has an important impact on other faults in the area. The latest activity of the Tan- Lu fault zone to the south of Mingguang fault zone occurred in Middle Pleistocene and thus the latest activity of the Huaiyuan—Chihe fault intersecting with the Tan- Lu fault zone also occurred in Middle Pleistocene. This may be the tectonic background in the Bengbu—Fengyang area where small and medium earthquakes dominated.