In this paper, the influence of the final rolling temperature and final cooling temperatures on the microstructure and properties of HG550 girder steel was investigated using a RALΦ450×450mm hot rolling mill. The OM, SEM and tensile tests were used to characterize its microstructure and properties. The results show that a reasonable combination of higher strength and good plasticity can be obtained at a final rolling temperature of 890°C and final cooling temperature of 620°C. Finally, its tensile strength can reach to 910MPa and the elongation is 24%.