Abstract: A mathematical model of hydraulic slotting with different nozzle axis spacing was established by using the Fluent software.It utilized the standard k-ε turbulent model to simulate the internal flow field,analyzed the influence of nozzle axis spacing on the flow field distribution,axis velocity decay and the pressure distribution of the borehole wall.The results showed that the influence was very great.The smaller the nozzle axis spacing was,the more disordered the flow field distribution was.With the nozzle axis spacing d increasing,the regularity of flow field distribution became clear,and the axial velocity decay decreased first and then increased.The best value of nozzle axis spacing is 40 mm.