Abstract: This paper mainly shows that discontinuities in the abutment of arch dam are measured by the means of sampling window, and orientation and trace length of discontinuities in the sampling windows are corrected and Mote-Cede simulated, thus the discontinuities' network models in 3-D space are formed. According to the project demand, the 3-D models are cut between a certain bandwidth, projected and calculated, therefore side structural planes' persistence ratio is acquired. On basic of the persistence ratio's results, rock mass quality of abutment is evaluated, and some theoretic data is offered for engineering design.