Abstract: The microstructure and hardness of precipitated hardening die steel 0Cr3Ni3MoCuAl with solution-treated at 860~1010 ℃ for 35 min and aging treated at 450~560 ℃ for 3 h are tested and studied.The results show that when the solution treatment temperature is 950 ℃,the holding time is 35 min and air cooling to room temperature,the HRC hardness number is up to 39.5,the structure is granular bainite and low carbon lath martensite and a small amount of residual austenite.When the aging-treated at 500 ℃ for the holding time 3 h and air cooling to room temperature,the HRC hardness number is up to 44.1 and the microstructure is tempered bainite.