Abstract: Joints are modeled by displacement discontinuity elements following the Mohr-Coulomb criteria, A nonlinear analysis method using constant matrix is suggested.Two corrections, i. e. making the fictitious load statically equilibrium and taking the element average value instead of mid point value as the influence coefficient, are adopted for increasing the precision of calculation.A numerical analysis of deep stability for a gravity dam model is given. The results of calculation are satisfactory and comparable with the model test.