Abstract: The batch brittle fracture causes of 3Cr20Ni11Mo2PB steel gas valves were analyzed by means of mechanical properties test, hardness test, metallographic examination and fracture analysis. The result show that the brittle fracture of the gas valves was mainly caused by the serious over-heated and partial over-burnt structure, which greatly reduced the plasticity and toughness of the gas valves because of the high solution temperature.