Disclosed are an ultrasonic surgical instrument (100) and ultrasonic surgical system； the ultrasonic surgical instrument (100) includes a waveguide (1) rotatable around an axis and in threaded connection with a transducer (200)； a force transmission mechanism is in fixed connection with the waveguide (1), which has at least one stress surface (41)； a rotatable mechanism includes a pushing mechanism and a rotatable driving mechanism having at least one force applying surface (51), the applying surface (51) and the stress surface (41) are not perpendicular to the axis, and can be engaged with each other； the pushing mechanism provides a pushing force the rotatable driving mechanism towards the force transmission mechanism, and the rotatable driving mechanism can overcome the pushing force when interaction force between the applying surface (51) and the stress surface (41) is in excess of a predetermined value.
