The causes include unqualified quality of gold treatment, improper nitriding process, large amount of grinding before nitriding, too high nitrogen content on the surface, high quenching and tempering temperature, overheating and decarburization on the surface. The countermeasures include selecting qualified materials, improving process, reducing grinding amount and grinding in several times, strictly controlling ammonia decomposition rate, re quenching and tempering after normalizing, and removing decarburization layer.