Abstract: To study the impact of water injection pressure to soft coal characteristic, impacts of pore water pressure generated by different water injection pressure to vertical stress, horizontal stress, compression ratio of coal seam, plastic zone of coal body in front of working face were simulated and analyzed by using FLAC3D finite difference program, influence rules of pore water pressure to charactersitcs of coal body were obtained, it can be seen, increase water injection pressure appropriately is benefit for the stable of coal wall.

Key words: Pore water pressure, Vertical stress, Horizontal stress, Compression ratio of coal seam, Stability of coal wall