The Longhekou Reservoir is a very important water source for the Chaohu Lake. Clay minerals from core ALE in the Longhekou Reservoir were analyzed qualitatively and semi-quantitatively. The result shows that the clay minerals are mainly chlorite (Ch/V), with many years' average quantity being 40%, subordinately kaolinite and illite, and minor smectite. 40 years' average quantity of illite in the reservoir is only 21%, lower than that of the surface sediments in the Xiaotian River (54%) and in the Huashi River (63.5%). The percentages of clay minerals in the Longtan River are similar to those in the Longhekou Reservoir,but obviously differ from those in the Xiaotian River ane Huashi River. The physiognomic and geological features have a strong impact on the surface sediments in the Longhekou Reservoir basin, and the sediments of the Longhekou Reservoir have an intimate relationship with the environmental dynamic forces and the features of clay mineral crystallization. The results also show that the clay minerals from the Laolong River have exerted an obvious effect on the reservoir sediments, and this is very important in the control of soil erosion.