The effect of heat treatment process on microstructure and mechanical properties of bearing steel was studied, and the mechanism of strengthening-toughening of the steel was also discussed. The results show that, with the increasing of quenching and tempering temperature and the number of tempering, as well as the use of acryogenic technology, the strength and hardness of carburizing bearing steel increases and the impact ductility decreases. Quenching at 910℃ and tempering twice at 180℃, the mechanical properties of bearing steels can reach HRC is 452, Rm is 1450MPa, ReL is 1240MPa and AKU is 105J; Residual austenite quantity can be controlled less than 1%. The better match of strength and toughness is attributed to grain refinement, ultra-fine martensitic variants, and large number of fine dispersed carbides. The dimensional stability of the steel is due to the control of the content of residual austenite.