How to effectively transfer and exert a pressure on drills in lateral drilling, and to raise the efficiency of rock-breaking and rate of penetration in a bid, is the key technology to improve the quality, speed and economic benefits of lateral drilling. Therefore, based on high pressure jet of 16-hole and 7-hole nozzles, which are suitable for lateral drilling in oilfield at the present stage, we carry out a research on the hydraulic calculation of high pressure water jet flow and the mechanism of rock-breaking. We use three-dimensional modeling software to establish models, and analyze the high pressure water jet velocity field combined with numerical simulation software. According to different injection, we calculate the local head of the two nozzles when the working fluid is pure water and the liquid-solid two phases of 4% solid content respectively, through the simulated relational expression between the local head and the injection rate to calculate the maximum speed of each hole and to ensure rock-breaking critical injection of 16-hole and 7-hole nozzles, then compare and analyze the rock-breaking effect of these two kinds of drill bits, at the same time to analyze the influence of nozzles angle on the effect of rock-breaking, so as to optimize the perfect angle of the nozzle and to provide theoretical basis for the popularization and application of lateral drilling high pressure jet rock-breaking.