Abstract: In order to improve bottom-hole jet-assisted rock breaking ability while drilling horizontal section with PDC bit,the characteristics of impeller swirling jetting were studied.Using k-ε standard turbulent flow equation,the impeller swirling jetting flow field was simulated.The swirling intensity and discharge coefficient were used to evaluate rock breaking capacity.Numerical simulation results showed that the discharge coefficient and swirling intensity were optimal under the condition of blade twist angle 115°-140°,dimensionless length of straight tube 0.6-0.8,and the falloff angle 60°-70°,and the jet rock-breaking ability is the strongest.Those rock breaking tests showed that the hole diameter of impeller swirling jet was three times of that of straight jet under the same pressure drop,and the hole diameter was the maximum when the standoff distance was 7-11 times that of nozzle diameter.The studies above indicated that rock-breaking ability of impeller swirling jet was better than that of straight jet,and the rock breaking ability could be improved with the optimization of nozzle geometrical parameters.All these means could enhance bottom-hole rock cleaning and breaking effect,and also improve drilling efficiency of PDC bits.