The third generation automotive quenching & portioning(QP) steel is introduced,which adopted a simple C-Si-Mn alloy system and Nb,Ti micro-alloying. The influence of partitioning process,such as partitioning temperature and time,on microstructure,mechanical property,work hardening behavior and bake hardening property of QP steel are studied. The process of quenching and partitioning in bainite zone (QP-B) is also investigated. The result shows that the prior austenite grain size decreased effectively via micro-alloyed. A triphase microstructure of martensite+bainite+austenite with a high austenite volume fraction of 7.81% is obtained by the QP-B process,the product of strength and ductility reached 31.6 GPa·%. The excellent work hardening property of Q&P steel is related to the volume fraction of retained austenite,which can be controlled by optimizing the partitioning process. The bake hardening value of the studied Q&P steel (0.24C-1.5Si-2.1Mn-0.05Nb) decreased from 80 MPa to about 30 MPa with the increase of partitioning temperature and time.