Abstract: Quartz-epidotization alteration is an important geological problem in Dagangshan hydropower station. Taking into account the advantage of geological survey and laboratory experiment, this paper analyses its geological distribution, mineralogical and structural characteristics and physical and mechanical properties. The study reveals that ranite in SN/E∠17°~26° low-angle shearing belts often develops quartz-epidotization alteration formed by the dynamic metamorphism, which always grows scratches and order step. Alteration produces sericite, chlorite, epidote and calcite weak mineral content of about 18%. Chemical analysis shows little change in its composition. Physical and mechanical tests show that the physical and water properties and strength characteristics of altered rock have a certain degree of weakening, natural and saturated compressive strength loss rate of 8.3% and 5.9%. Quartz and epidote produced by alteration have an impact on the shear strength of the structure. In-situ direct shear tests show shear intensity decreases. Research has some innovative, can be a reference on engineering impact and process of quartz-epidotization alteration.