Exploring the mechanical response and damage mechanism of fractured rocks under hydro-mechanical coupling is one of the important ways to solve the safety and stability problems of rock engineering under hydro-mechanical coupling conditions. Based on Biot porous media theory and elastic theory, a numerical simulation method of hydro-mechanical coupled phase field is developed, and a staggered time integration scheme is proposed to obtain stable solutions of fluid pressure and solid deformation, in which the obtained control equations adopt the volume strain separation and partial strain separation of elasticity theory of fully saturated porous media. Two different numerical examples of fluid permeability tests and hydraulic fracturing with natural fracture interaction are used for validation. By the comparing of the numerical model with the analytical solution, the numerical results and the previous data are in better agreement, which verifies the validity and correctness of the model method. In addition, in order to investigate the unloading damage mechanism in the actual engineering excavation process, a hydro-mechanical coupled unloading damage model was established by combining numerical examples of borehole injection tests to simulate the whole process of fracture rock propagation damage under the dual conditions of hydro-mechanical coupling and surrounding pressure unloading. The study shows that mixed tensile-shear crack expansion and connection dominate the final damage mode during coupled hydro-mechanical unloading damage. Confining pressure and initial unloading stress states have a promoting effect on the development of shear cracks, while water pressure is reversed.