Abstract: The loss of Ti, a key strengthening element of 00Cr12Ni9Mo4Cu2TiAl martensitic stainless steel during electroslag remelting was studied. The effects of different chemical composition and different heat treatment processes on the microstructure and hardness of the test steel were discussed. The results show that, using the "control Al to protect Ti" technology, after the remelting process of electric slag, the element content of Ti and Al is stably controlled, and the loss rate is reduced to less than 4%. The hardness of the test steel increases with Ti content increasing. At a Ti content of 1.2wt%, the optimal aging reinforcement temperature is 450 ℃ for 120 min. The trace elements V and Nb can reinforce the material. After1100 ℃/1 h solid solution+450 ℃/2 h aging treatment, the test steel can get more excellent microstructure and hardness. At the same time, it also has a variety of strengthening mechanisms of phase change hardening, processing hardening and aging strengthening. Among them, the aging reinforcement has the greatest impact on the test steel, and the hardness is increased by220 HV, accounting for 47.8% of the total hardness increase.