Abstract: 34CrNiMo6 blanks cracked after forging and tempering. The cracking reason of the 34CrNiMo6 blanks was analyzed by macroscopic fracture observation, SEM morphology observation, chemical composition analysis, metallographic examination and hardness test. The results show that the crack starts in the forging process. And it continues to expand during the later quenching process, eventually leads to cracking failure.