In view of the major safety problems of floor water outburst induced by atructure activation in the process of deep coal seam mining under pressure, taking No.152 lower 40 Face of Jiulong mine in typical deep mining under pressure in Hanxing mining area as the research object, which still had floor water outburst after regional control, the geological and hydrogeological background of the working face and its water disaster prevention and control work were systematically analyzed, and the water outburst source, water channel and disaster-causing inducement were clarified. The mechanism and prevention and control technology of floor water outburst under the synergistic effect of large mining depth, high pressure and complex structure were studied. Based on the research results of engineering practice, a three-dimensional prevention and control technology for deep complex structural conditions was proposed, and the three-dimensional oblique horizontal branch hole technology was used to supplement the fault fracture zone. After grouting and plugging, the water inflow of the working face was reduced to 0, which showed that the technical system could improve the safety of mining under pressure in the working face and provide technical guarantee for safe and efficient mining of deep coal seams.