Abstract: Based on the isothermal treatment and continuous cooling test of an Mn-Cu-Nb-B low carbon bainitic steel, it was found that several types of intermediate transformation could be formed in the range of 500-700℃. Cooling rate and finish cooling temperature have much effect on the final microstructure and mechanical properties of the steel. When the finish cooling temperature was selected around 630℃, a proper combination of quasipolygonal ferrite, granular bainite and fine M/A could be obtained. The yield stress of this type of microstructure could reach 600 MPa, with a better plasticity and low-temperature impact toughness. A proper control cooling process influences the intermediate transformation products, in this way the mechanical properties of a low carbon bainitic steel can be fairly optimized.