The invention discloses an in-cavity torsional vibration ultrasonic lithotripter, which comprises a casing, an ultrasonic transducer, an amplitude-change pole, a water pipe connecting pipe, a negative pressure suction device, an inner catheter, an outer catheter and a step annular frequency regulator, wherein the ultrasonic transducer is accommodated in the casing, the amplitude-change pole is connected with the front end of the ultrasonic transducer, the water pipe connecting pipe is connected with the tail end of the ultrasonic transducer, the negative pressure suction device is connected with the water pipe connecting pipe, the front end of the amplitude-change pole is of a spiral groove structure, the inner catheter and the spiral groove are connected through screw threads, the step annular frequency regulator is connected onto the inner catheter through screw threads, and the outer catheter is connected onto the step annular frequency regulator through screw threads. The high-frequency torsional vibration and the low-frequency ultrasonic vibration are combined to be applied into the stone breaking process, the consumption on a lithotripter tool head can be reduced, the stone breaking efficiency is improved, the impact force and the tissue damage in the stone breaking process are effectively reduced, and the injury to the human body tissue due to ultrasonic cavitation and the like can be effectively avoided.