Abstract: In respect to properties deterioration of casting 10CrNi3MoV steel after thermal processing and normal temper,heat treatment technical tests of cycle quenching or subcritical quenching was performed,and mechanical properties,microstructure and grain size of the steel were investigated.The results showed that a new quenching and tempering technology,austenitizing at 835℃ for 2h and subcritical at 820℃ for 2h and then tempering at 630℃ for 3h,could refine grains of steel effectively,low temperature toughness was significantly improved,therefore a better matching of strength and toughness was obtained.