Abstract：The coaxial swirling dual-jet inherits both the large impact area and deep penetration depth of swirling jet and round jet respectively，which is generated by placing a coaxial round jet at the axis of annular swirling jet. Under high confining pressure，the cavitation incepted by strong shear of the two jets can enhance breaking rock efficiency. Three parameters，nozzle distance，jet pressure and ambient pressure，are studied and the rock breaking mechanism is deduced. The experiments demonstrated that the rock breaking volume increases first then decreases with the increasing of nozzle distance，so an optimal nozzle distance exists¢ which is 13 times of equivalent nozzle diameters. Nozzle distance also has great impacts on the rock penetration depth. With the increasing of nozzle distance，the penetration depth increases first then decreases. The rock breaking area is affected by nozzle distance too. With the increasing of nozzle distance，rock breaking area has almost linear increasing trend. The increasing of jet pressure can largely increases rock breaking volume. When the jet pressure is below than 15 MPa，the rock breaking volume hardly increases；when the jet pressure is over 15 MPa，the rock breaking volume greatly increases. Penetration depth was largely increased with the increasing of jet pressure. The rock breaking area was insensitive to jet pressure. The rock breaking volume and penetration depth will sharply decrease with the increasing of ambient pressure. But the rock breaking area is insensitive to confining pressure. The rock breaking of coaxial swirling dual-jet is a combination of cavitation erosion，jet erosion，shear breaking and pressure pulsation breaking.
