Abstract: In order to improve the coal rock-breaking capacity of water jet and pressure-relief and permeability effect, by establishing the impact dynamic pressure model of high pressure gas-liquid two-phase jet,the key parameters were obtained which affected the capacity of coal rock-breaking. Experimental tests about the characteristics of impacting coal rocks were conducted by self-designing rock breaking test system of high pressure gas-liquid two-phase jet. The results showed that the rock breaking threshold pressure was reduced by 50% ,the breaking depth increased 25% ,the diameter was 2 times and the efficiency increased about 80% by comparing with pure water jet. The coupling between the gas-liquid-solid three phases resulted in breaking coal:the structure of jet was changed and formed local impulse by mixing gas,which strengthened coal rock-breaking ability;cracks were motivated under high pressure liquid pulsa- tion,which promoted by multilevel collapsing of tiny gas phase. By the multilevel alternation of liquid pulsation and gas phase,the coal rock was broken finally when the original cracks were connected.