Abstract: The microstructures of C-Si-Mn steel by the quenching and partitioning (Q&P) treatment was studied by scanning electron microscopy and X-ray diffraction, and then the effects of partitioning temperatures on mechanical properties and fracture morphology of the steel were analyzed. The results show that with the increase of the partitioning temperature, the martensite in the experimental steel was gradually transformed from quenched martensite to tempered martensite, and the tensile strength of the steel decreased while the elongation increased. The product of strength and elongation reached the maximum value of 23 366.64 MPa·% at the temperature of 420 ℃. The elongation changing with partitioning temperature trend of the experimental steel coincided well with that of retained austenite content. The volume fraction of retained austenite reached the maximum value of 14.4% at 420 ℃, meanwhile the elongation reached the maximum value of 23%. With the partitioning temperature increase, the fibrous area at the tensile fracture surface of the steel enlarged while the radial area decreased, and the number of dimples at the fibrous area increased constantly.