Along with the over exploitation of oil and gas resources, complicated reservoirs should be exploited in abominable environments. New drilling methods, drilling tools and drilling crafts for breaking rock are urgently needed. In drilling project, opening radial holes in the wall of self-excited oscillation cavity, more drilling fluid absorbed from annulus and more hydraulic energy could be obtained to break rock efficiently. Therefore, in this paper, self-increasing flux of cavity with different velocity in annulus, ratio of upper and lower nozzle diameters and diameter of aperture were simulated using CFD numerical method. Then flow fields in different aperture conditions and the best aperture parameter were obtained. Some references can be provided to actual drilling for further better jet breaking rock and improving drilling speed, which also have a good economic benefit.