Abstract: Ultrasonic impact treatment was conducted on as-cast semi-high speed steel with surface presetting chrome powder, and then the steel was annealed at 450℃ for 2 h. The microstructure and high-temperature (450℃) wear resistance of the surface layer before and after treatment were studied. The results show that the as-cast structure of the tested steel consisted of sorbite and carbides. After ultrasonic impact and annealing treatment, the cemetite lamellae in sorbite was broken and spherized, and the structure of the surface layer was refined. After ultrasonic impact and annealing treatment, the surface hardness of the tested steel increased, the hardness in the surface layer distributed in gradient, and the thickness of the hardening layer reached 2.5 mm. Moreover, the high-temperature wear resistance was improved; the wear rate decreased from the as-cast 0.997 mg·min^-1 to 0.640 mg·min^-1, the friction coefficient decreased from the as-cast 0.547 to 0.509, and the abrasive wear degree also decreased.