Abstract: In order to obtain the effect of temperature on fracture toughness of the SA508-Ⅲ weld metal, the constitutive curve method (CCM), ASTM and ISO standard were applied to determine the fracture toughness of weld metal in typical temperature points. The fracture toughness value obtained from CCM showed a reduction trend with the increase of temperature. When the temperature increased from 20℃ to 100℃ and from 100℃ to 320℃, the fracture toughness value were reduced to 11.1% and 5.4%, respectively. SEM fracture photographs of Compact Tension specimens revealed that the tested SA508-Ⅲ weld metal presented ductile fracture at test temperature points. However, when the temperature reached 100℃ to 320℃, dimples became shallow and small, which led to the decrease of fracture toughness. Moreover, this study also found that the fracture toughness obtained from CCM was the same as that of ASTM standard at 20℃ and 100℃, and intermediate between that of ASTM and ISO at 320℃.