Abstract: Based on the BS7448 standard,the crack tip opening displacement (CTOD) tests were conducted on the weld metal and heat-affected zone (HAZ) of DH36 steel joint,which was made with submerged arc welding (SAW) process and then followed by post weld heat treatment (PWHT),to investigate the influence of PWHT on fracture toughness. The results demonstrate that PWHT did not always produce positive effects on fracture toughness of weld metal. Especially,PWHT had negative influence on fracture toughness of HAZ with coarsened grains, and the CTOD values in coarsened HAZ decreased. After PWHT,the CTOD value of weld metal from 90 mm thick specimen slightly descended,while that from 60 mm thick specimen obviously increased. The CTOD value of HAZ from 90 mm thick specimen descended severely,while that from 60 mm thick specimen descended slightly.