Abstract: Fractures in large-scale engineering works such as dams and tunnels have long gained attention because they concern safety problems of engineering works such as the strength of rock masses.There mainly occur carbonate rocks with minor clastic rocks at the dam site of the Goupitan Hydropower Station,Wujiang,Guizhou,and the NE,NW,N-S and E-W sets of structural fractures may be recognized in the rock sequences.However,80 percent of the fractures have been healed by three phases of calcite veins,thus greatly reducing water permeability and increasing the strength of rocks.Some fractures have not been filled or re-opened after filling,of which bedding-parallel slip fractures are throughgoing to a certain extent,to which attention should be paid in engineering works.