Directional drilling under coal mine is an important technology to realize efficient gas extraction and prevent flood water inrush. The method of rotary drilling is mostly adopts. In hard rocks, low drilling efficiency, long drilling cycle and high construction cost seriously affect the project progress and quality of gas extraction drilling. The drilling test results of the limestone strata of Zhaogu mine1 show that with reasonable control of pump pressure, rotary speed and weight on bit, the efficiency of impact rotary drilling by SC86H high energy liquid-jet hydraulic hammer is increased by 3 times than that of conventional PDC rotary drilling, and the drilling cost is saved.