Abstract: The fan blades of a Q235A steel cracked after running for about 180-500 h. The reason of cracking was analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination and hardness test. The results show that the crack originated from the heat affected zone at the weld edge on both sides of the blade root. Under the action of alternating stress and welding stress generated by the rotation of the fan and the overall vibration of the generator, the crack initiated and propagated, which eventually led to the crack of the blade.