Abstract: A Cr12 steel cold work die cracked during WEDM process. Fracture reason of the die steel was analyzed by means of the microstructure examination,scanning electronic microscope fracture analysis,chemical compositions analysis and hardness test. The results show that the cracking of the Cr12 steel die was due to brittle fracture. Chromium content exceeding the limit and deficient forging made the eutectic carbides in the die material were numerous,coarse and seriously aggregated network-like distribution,so the eutectic carbides became stress concentration source and initiated cracks,and then under the combined actions of machining stress and internal stress the cracks extended and finally resulted in the cracking of the die.