Abstract: The copper alloy air valve of truck tires in the use of 1~3 months later had cracked partly. The cracking reasons was investigated by means of macroscopic examination, chemical composition analysis, metallographic examination, hardness testing, fracture analysis and energy spectrum analysis.The results showed that the air valve cracking was stress corrosion cracking under the union action of stress and environment medium; the reason was stress relief annealing was not done to the air valve after cold working deformation.