Abstract: The steel of 2.25Cr-1Mo-0.25V was welded by manual arc welding,the composition of weld seam and its impact energy were tested,and the microstructure of welded joints and the initiated cleavage crack were analyzed and investigated.the weld samples with lower impact energy were treated to decrease the embrittlement.The research results show that weld seam with lower impact energy has more content of Mn,Si,Mo and other impurity elements.The elements such as Mn,Si,and Mo accelerate impurity elements segregated at grain boundaries.The impurity segregation on grain boundary decreases the properties of grain boundaries and the specimen fails as the intergranular fracture, so the impact energy value decreases.After the reduction of embrittlement treatment,the impact toughness will be recovered, and weld seam has high temperature temper brittleness.The reason of temper brittleness is that the content of impurity elements segregation on grain boundary.Based on the above-mentioned results,so the welding electrode for 2.25Cr-1Mo-0.25V steel was developed,the content of Mn,Si,Mo and impurity were strictly controlled.