Automobile beam steel with high strength is the development trend of the automotive industry, which will help to conserve resources and protect the environment. The crossbeam as an important part of the frame, its strength also affects the overall strength of the frame, which will affect the safety performance of vehicles. At present, the crossbeam steel of heavy-duty vehicles is mainly Q235B and Q345C. About 3% of the crossbeams occur cracking problems when heavy-duty vehicles drive about 10000 km or about half a year or so. The strength increasing will cause the cracking in the forming process. Therefore, it is of great significance to develop a high strength crossbeam steel with high fatigue and high formability. In this work, the microstructure, properties and strengthening mechanism of 600 MPa grade Nb-Ti microalloyed high formability crossbeam steel were investigated by OM, SEM and TEM. The results show that the finish rolling temperature has a considerable influence on the microstructure and mechanical strength, with the decreasing of finish rolling temperature, the ferrite grain size and the size of precipitates decreases gradually; dislocation density, the number of precipitates and the ratio of Nb/Ti increase gradually; both the yield strength and tensile strength increase monotonously, while the elongation has an optimum temperature. The optimal mechanical properties were obtained when the finish rolling temperature is 840 ℃, and the yield strength, tensile strength, elongation and impact energy at -60 ℃ reached 541 MPa, 615 MPa, 31.0% and 117 J, respectively. The NrT and PTT curves of (Nb, Ti)C precipitated in the austenite showed that the nucleation rate of uniform nucleation and dislocation linear nucleation increases and the nucleation time is shortened with the decrease of temperature in the experimental temperature range, which is consistent with the observation result that the size of precipitates decreases with the reduction of the finish rolling temperature, while the number of precipitates increases. The grain refinement strengthening and dislocation strengthening are the main strengthening modes of the steel, the grain refinement strengthening accounts for 46%~48% of the yield strength, the dislocation strengthening accounts for 18%~25%, while the precipitation strengthening only contributes 2% of the yield strength.