Abstract: The vertical quenching-cracking of DJ4 spring was investigated through surface form,metallograph,hardness test and impact fracture analysis. The results show that the surface flaws,decarbonization and inclusions are the induced factors;over-high austenitizing temperature promotes growth of the origin austenite grains of the steel and infirmness of grain boundary is the main reason. The vertical crack is avoided by adjusting the heat treatment process and recrystallization cooled to 600℃ after hot-forging,which make the fracture toughness property of impact improve greatly.