Abstract: The quenching cracking reasons of rack track gears were analyzed by means of macro examination, chemical composition analysis, metallographic examination and hardness test. The results indicate that the cracking property of the rack track gears was scaled cracking, and the poor carburization quality and improper cooling velocity were the main reasons for the quenching cracking of the rack track gears. Some improvement measures for the heat treatment of the rack track gears were proposed finally.