This open access book is divided into seven chapters. Within those seven chapters, the WRI problems that may occur in coal mining environments were summarized, strength weakening of the rock and its micromechanism in WRI were analyzed, an accurate characterization method of pores and various minerals were proposed, the mechanical characteristics and damage mechanism of sandstone under long-term immersion were studied, the simulation methods of fluid solid coupling for water immersion weakening are proposed, and the feasibility of the simulation method is verified by simulating surrounding rock weakening in water filled fracture structure roadway and the failure analysis of residual coal pillar under the coupling of mining stress and water immersion. This book can provide guidance, experience and reference for scientists and engineers who work in mining engineering, civil engineering, and geotechnical engineering.