Based on the assumption of least energy dissipation, a general expression of flowing criterion of plastic strain is derived. This formula has a cross couple term of current stress and a plastic softness increment matrix that do not exist in the classic plastic flowing criteria. Due to this cross couple term, the plastic deformation does not always flow along the normal direction of yield function surface, making the intrinsic mechanism of shearing dilation characteristics for quasibrittleness material well discovered. With the plastic strain flowing equation, increment iteration is conducted. The evolvement process of plastic deformation for soil sample subject to axial and surrounding pressure is then simulated. The fracture form of the simulation is similar to the experimental results. Finally, the slippage fracture process of a soil slope is modeled with the flowing criterion of plastic strain. The fracture form conforms to the practical case, showing that the flowing rule is rational and reliable. Therefore the numerical method based on the new flow rule has a good prospect of applications.