Abstract: Standard fracture toughness measurement was explored on contact tension specimen made of ductile metal S355 used for nuclear plant structure. During the test, plastic collapse instead of crack extension occurred ahead of crack tip with increasing tension load and only local area around crack tip yielded when the whole specimen failed. After that, Gurson model was used to simulate the failure process of contact tension specimen made of S355. The calculation results show that Gurson model can reproduce crack tip collapse well. At last, a universal failure assessment curve was built for S355 by combining finite element simulation with test measurement, and relationship between plastic failure load and crack length was determined.