Abstract: Based on uniaxial tensile tests, the real stress-strain data is obtained to determine the parameters of the hardening model through curve fitting. This method is widely used to establish the stress-strain relationship for metal thin plates. However, the extrapolation results of the hardening model may vary depending on the chosen model and parameters. Therefore, it is crucial to accurately assess the applicability of the hardening model under significant deformation for CP1180 ultra-high strength complex phase steel. The uniaxial tensile test is used to obtain the true stress-strain date of the material. The curve is fitted at room temperature based on Hollomon, Lian, Swift, Hockett-Sherby and Swift/Hockett-Sherby respectively, and then five hardening models are established. To verify the accuracy of the five models, the combination of the hydraulic bulging test and DIC online detection technology are used to obtain the true equivalent stress-strain date under large strain at vertex of bulging part. The bending test and finite element simulation analysis are conducted on the ultra-high-strength steel plate CP1180 with a thickness of 1.48 mm. The results show that：the maximum plastic strain in the tensile direction after the bending test of the plate is 0.249 3, while the strain calculated by the Swift/Hockett-Sherby (a=0.4) model is 0.253 56，with a deviation of only 1.68%, which had the highest prediction accuracy.

Key words: ultra-high strength complex phase steel CP1180, hardening model, bending, finite element simulation