Based on the characteristics of water jet technology,such as environmental protection,easy access to materials and strong cutting ability,we propose a method of using water jet to cut reefs.By establishing a two-dimensional plane mathematical model,we simulate and calculate the motion characteristics of high-pressure water jet under submerged condition.The results show that the initial section of the jet is the region where the jet impingement velocity is the largest,the dynamic pressure is the largest and the energy is the most concentrated.The submerged water depth is from 0 m to 30 m,with the increase of water depth confining pressure,the initial stage velocity attenuation is less than 5 m/s,and the attenuation degree is only about 1.5%.In the submerged environment of 0 m/s to 5 m/s,the impact of water flow on the initial stage of the jet is relatively small.The variation of horizontal velocity component in the initial stage of the jet is only within 8.5 m/s,and there is no obvious deviation,so it still has a good impacting flow pattern.