Abstract: The single-pass compression test of HG700 automobile beam steel was carried out using a Gleeble 3500 thermo-simulation machine, and the flow stress behavior at deformation temperatures of 950-1 150℃ and strain rates of 0.01-5.00 s^-1 was investigated. Based on true stress-true strain curves, the flow stress constitutive model of the steel was established by linear regression method, and was verified by tests. The results show that the dynamic softening behavior of HG700 automobile beam steel was dominated by the dynamic recovery at high strain rates (1.00,5.00 s^-1); the dynamic recrystallization of HG700 automobile beam steel occurred obviously at low strain rates (0.01,0.10 s^-1). Both the increase of deformation temperature and the decrease of strain rate would promote the reduction of flow stress and the early arrival of peak stress. The prediction results obtained by the flow stress constitutive model with the variables of deformation temperature, strain rate and true strain agreed well with the test results, indicating that the model could predict the flow stress of HG700 automobile beam steel accurately.