Abstract: In order to meet the low temperature requirements of medium strength low alloy cast steel in high and cold region, the composition optimization of B+ grade steel was carried out according to the influence of alloy elements on ductile brittle transition temperature. The effects of three different heat treatment processes on the low temperature impact properties of the material were investigated. The effects of niobium content on the mechanical properties and microstructure of the material were studied by combining theory with experiment. After normalizing pretreatment, quenching and tempering treatment, the impact energy absorption of the low alloy low temperature resistant cast steel can reach 20 J at −60 ℃, whitch meets the performance requirement. When the Nb content is 0.04%, the microstructure is uniform, the grain is refined, and the low temperature impact property is the best.