The invention relates to a probe assembly used for ultrasonic inspection of a heat-transfer pipe of a steam generator. The probe assembly comprises ultrasonic probes, a probe clamp and a guiding head, wherein the probe clamp is of a cylindrical structure, and the external diameter of the probe clamp is slightly smaller than the internal diameter of the heat-transfer pipe of the steam generator; a plurality of probe installing holes are arranged along the axial direction of the probe clamp at an equal interval and penetrate the probe clamp along the radial direction of the probe clamp, and the ultrasonic probes are embedded in the probe installing holes; the probe clamp is further provided with a cable hole which is communicated with one axial end of the probe clamp; two petals are respectively snapped at two ends of the probe clamp and are plastic hollow petal self-locking joints; the maximum external diameter of the petals in expansion is slightly greater than the internal diameter of the heat-transfer pipe of the steam generator; the petal, far way from of the end with the cable hole of the probe clamp, on the probe clamp is connected with the guiding head; and an ultrasonic cable is threaded into the cable hole from the petal located at the end, provided with the cable hole, of the probe clamp and is then connected with the ultrasonic probes. The probe assembly provided by the invention is used for inspection of the heat-transfer pipe of the steam generator, especially for inspection of a special structure of a transition zone of an expand tube.