In order to reduce quench deformed of car gear, a new kind of microdistortion gear steel is developed and its fine microstructure is discussed by SEM. The results show that the tested steel can obtain carbide free bainitic ferritic laths with fine microstructure under air-cooling condition. The bainitic ferritic laths, sublaths and subunits are surrounded by retained austenite, which can insure the gear steel possesses high strength and toughness, the impact toughness has increased remarkably. The good mechanical performance of the steel can meet the service demands of the gear.