Abstract:According to practical working situation,nonlinear dynamic finite element method is adopted to establish a numerical model of combined breaking rock with high pressure water jet and mechanical bit. Breaking process of rock with high pressure water jet is studied;and two critical pressure concepts are put forward. The conclusion that rock breaking process under high pressure water jet is divided into hammer impacting break and erosion break is proven by experiment to be true. Conclusions can be drawn from calculation results that the efficiency of the combined breaking rock is about 2 times as much as the summation of high pressure water jet and mechanical bit separately breaking rock;and the best distance between water jet and bit is about 13 mm. When the pressure of jet is high enough,the efficiency of breaking rock will be increased if rotation speed improves. Dropping down the drilling pressure properly to a certain value will not affect the efficiency of breaking rock. Hydrostatic pressure reacts on the efficiency of breaking rock.