Abstract: In this paper, based on the structural anisotropy characteristics of coal body, crack development of crack initiation, propagation and stop by water injecting into coal body is numerically analyzed in microscopic model. The results show that the stress at the joint end of coal body is concentrated during water injection, and then propagates along the joint surface (weak surface). As the shear stress is less than the shear strength of coal surface, the crack stops. When the water injection pressure is higher, the coal body not only propagates along the joint surface, but also causes the coal body damage at the crack tip, which leads to a new crack path.