Abstract: Many pits were found on the tooth surface of high-speed gear shaft in the blasting shot treatment process after the gear shaft was carburized,quenched and tempered. Optical microscope,scanning electronic microscope,direct-reading spectrograph and microhardness tester were employed to analyze the pits. The results show that intercrystalline-extended micro cracks existed on the pit zone of the tooth surface,and there was intercrystalline-distributed carbide at the same time. “⊥”type cracks were generated on the surface after carburized in the process of air cooling. “⊥”type cracks expanded longitudinally to form decollement crack during the subsequent storage period and isothermal quenching,broke and sloughed in the process of blasting shot,then the pits appeared.