In order to solve the problem of frequent roof fall and coal spalling in fully mechanized caving stope of No.4 coal seam in Majialiang Coal Mine, by means of laboratory test and numerical simulation, the study of water content influence on the physical and mechanical properties of coal was carried out, and the coal spalling prevention and control technology by coal seam water injection was studied. The results showed that the peak compressive strength of coal samples in No.4 coal seam decreased with the increase of water content, and the peak strain increased with the increase of water content. After water injection, the depth of coal wall spalling could be reduced by 44 %, which proved the feasibility of spalling prevention and control technology by coal seam water injection. Based on this, a detailed dynamic pressure water injection scheme was designed. After the practical application of No.14206 fully mechanized caving face, the range and frequency of coal wall spalling in the working face were significantly reduced, and the ideal engineering application effect was achieved.