Abstract: CTOD test is conducted with die casting and batches of continuous casting 10CrNi3MoV steel plates and the relation between CTOD characteristic value and center line segregation is analyzed. The results show that the resistance of die casting plate to crack forepart propagation is higher than that of continuous casting plates,but to crack unstable extension,the later is no lower than the former and the line segregation will results in CTOD value falling, so the carbon content in continuous casting 10CrNi3MoV steel shall be controlled at a level no more than 0.11% or some other measures shall be adopted to decrease the segregation for good fracture toughness of the steel.