In accordance with the demand for reduced fuel consumption and CO2 emissions in automobiles, and with the increasing high demand for vehicle lightweight and safety, advanced high- strength steels (AHSS) have received more attentions in recent years. The recent trend for the development of AHSS has been concentrated on the complex microstructure with multiphase. Quenching and partitioning (Q&P) steel with carbon-enriched austenite within martensitic matrix as a competitive candidate of AHSS have been developed widely. It has high strength and good ductility depending on the multiphase microstructure. Therefore, the relationship of the mechanical property and the microstructure of the Q&P steels should be studied in detail. In the present work, the microstructure characterization and mechanical properties of the experimental steel treated by one step Q&P process were investigated, as well as the direct quenching and Q&T processes. The results show that the microstructure of the steel treated by one step Q&P process mainly consists of lath martensite, plate martensite and residual austenite films between martensite laths. With a increase in the holding time, the fraction of the plate martensite firstly increases and then reduces, while that of the retained austenite firstly increases and then becomes constant. The combination of strength and elongation of the steel processed by one step Q&P is much better than the one processed by the other two, that is to say, the former one can possess good strength and ductility at the same time. The product of tensile strength and elongation, the tensile strength and the elongation can achieve 21774.2 MPa·%, 1442 MPa and 15.1%, respectively. Along with the holding time increasing, tensile strength decreases but elongation rises and finally be stable.