For 1800 MPa grade hot formed steel CR1200/1800HS for automotive body, its mechanical properties and constitutive model under dynamic loading were researched. Firstly, the mechanical properties of hot formed steel were obtained under six kinds of strain rates, and the variation laws of key mechanical parameters were analyzed. Then, the effective stress-plastic strain extension curve of the reference strain rate was obtained by using Voce+ and Hockett-Sherby hybrid hardening model, and the optimal parameters of the hybrid model were obtained by using bulging test and simulation benchmarking, which coupled with various strain rate variation coefficients to obtain the high strain rate material model. Finally, the accuracy of the model was verified by comparing and analyzing the impact test of door anti-collision beam and the simulation. The results show that the strain rate sensitivity of CR1200/1800 HS steel is relatively low. The maximum deviation of the effective stress at certain points of the high strain rate material model comparied with the test is less than 3%. The load-displacement curve obtained from simulation is consistent with the test results, and the deviation of the key parameters is within 5%, while the deviation using the quasi-static material model is about 9%. The results indicate that the accuracy of the high strain rate model constructed is high, which provides a reference for such collision analysis.