Abstract: In order to select the best injection parameters of water hydraulic extrusion,improve the outburst effect,the paper quantificationally analyzed the process of coal initiation,crack extension and extrusion under high pressure water infusion with the method of numerical simulation,studied the variation in water injection process of coal stress field,hydraulic gradient distribution field,displacement vector field around water injection hole by numerical simulation software RFPA2D.The relationships between the injection parameters and the other factors were obtained by simulating,which provided the basis for rational allocation of water parameters.