Abstract: The C-Mn-Si steel was quenched and partitioned at different partitioning temperatures, the mechanical properties and residual austenite contents were investigated, the microstructure was observed by SEM and TEM, and the effect of partitioning temperature on microstructure and mechanical properties was analyzed. The results show that the microstructure of the tested steel consisted of lath martensite with low carbon, nubby ferrite and banded residual austenite. The tensile strength of the tested steel took down trend with the increase of the partitioning temperature, and the change trend of elongation and residual austenite content was same, and the variation was uncertain. The increase of manganese content could stabilize residual austenite, and then raise the elongation of the tested steel. And the elongation was not sensitive to partitioning temperature.