A sheath assembly is adapted for an ultrasonic probe and includes a plug portion and a sheath portion connected to each other. One end of the plug portion of the sheath assembly is used for detachably and fixedly connecting with a connecting butt joint portion of the ultrasonic probe, so that the plug portion and the connecting butt joint portion are detachable after the ultrasonic probe is used. An inside of the plug portion communicates with an inside of the sheath portion to receive a torque transmitting portion of the ultrasonic probe.