Abstract: In order to perfectly consider the role of crack seepage in rock slope failure, on basis of numerical manifold method program with the function of crack propagation, the coupling mechanism of seepage and deformation is illustrated and the corresponding coupling equations are deduced from the viewpoint of minimum potential energy principle. The simulation of seepage and fracture is implemented in the program. This program is used to simulate the failure of rock slope with an initial crack under seepage load. The results show that the crack begins to propagate under the initial water pressure, and gradually runs through the rockmass to form the block. Therefore, the block breaks away the original rockmass under the action of gravity. Meanwhile, from the calculation of the stress intensity factor (SIF) in the crack propagation, it can be seen that the first SIF value is always larger than the second one. With calculation time going on, the difference between them becomes larger. Hence, the crack propagation is mainly the type Ⅰ mode.