Abstract: In this paper.the effect of austempering process on the microstructure nd properties of ADI has been studied. The results show that the uppet bainitic/lower bainitic mixture matrix can be obtained under the foulwing condition:880℃ Austeniting +320℃ Austempering. The mixture matrix has opt汕um integial mechanical propertise and fully meet the technological requirement of ADI gears of the automobire engine.