Abstract: After X12CrMoWVNbN10-1-1 steel was heated at high temperature for a long time, a lot of δ ferrites would separated out, which had larger effects on mechanical properties of the steel. Firstly, the original samples were re-treated, and then were heated to 1 000-1 100 ℃ for a long time or was treated with hot upsetting; finally, impact property was tested. The effects of heat treatment and hot upsetting on δ ferrites in tested steels were studied. The results show that heat treatment had not obvious effect on eliminating δ ferrite, and had limited improvement on mechanical properties. δ ferrite eliminated with the happening of recrystallization during hot upsetting, and residual δ ferrite was inversely proportional to effective strain, and mechanical properties of the steel improved obviously, too.