Abstract: In order to examine the water injection effect in the coal seam and optimize the technological parameters of water injection, study was carried out on four indicators of the water injection time, water increment, water injection pressure and injection range based on COMSOL5.0 water injection simulation data and by using the improved multi-index grey target weighted decision model, and by combining the actual conditions of No.2 Dongrong Mine, a series of calculations was made on the operator interval conversion of the indicator attribute. The calcullated results showed that the extraction of four indicators was reasonable and they could accurately reflect the effect of water injection; the resulting pressure falled in the range of the actual existing pressure (6 MPa to 16 MPa), the best effect of water injection was achieved; and the most ideal injection pressure was 15 MPa. The practice proved that the decision model was reasonable for the optimization of water injection parameters and it had a certain guiding significance to the engineering practice.