Abstract: In order to obtain accurate and reasonable plastic parameters of materials from the test curve of small punch test, a method based on simulated annealing particle swarm optimization algorithm and finite element simulation was proposed to obtain the elongation and section shrinkage of materials after fracture. Firstly, the load-deflection curves of X65 and X70 pipeline steel were obtained by small punch test. Secondly, the simulated annealing particle swarm optimization algorithm and finite element simulation were used to make the simulation curve of small punch test approximate to the test curve, and then Johnson-Cook (J-C) constitutive model parameters were identified. Finally, the identified parameters were used to simulate uniaxial tensile test, so as to obtain the elongation and section shrinkage of the material after fracture. The maximum relative errors of the elongation and section reduction of the two pipeline steels obtained by this method and the uniaxial tensile test results were 23.58% and 3.70%, respectively.