Fracture persistence is an essential parameter to evaluate the stability of rock mass. In the present paper，a projection method based on fracture network modeling was employed to study the three-dimension(3D) fracture persistence of abutment rock mass in Wudongde dam site. Fracture data from an exploration tunnel was used to generate a fracture network model. Subsequently in the fracture network, numbers of projection planes with different positions and different attitudes were set. A computer program was written to calculate 3D fracture persistence. The scale effect on persistence is discussed. The distribution characteristic of persistence values was analyzed. Also the change of lateral persistence with directions was studied. The following conclusions were drawn from the study：(1)The horizontal persistence values do not have a noticeable scale effect, while the effect of size on the lateral persistence is significant;(2)The lateral persistence values conform to a normal distribution with a mean value of 3.9;(3)The persistence value varies with the direction of projection plane. The steep dip angle corresponds to a low persistence value. A maximum value is obtained when the trend and dip angle of the projection plane are 175°and 65°.
