[en] Quenching and partitioning (Q and P) steel has bright prospects for applications in the automotive lightweight field. For predicting the optimal quenching temperature (QT) more accurately, a QT selection method modified by DICTRA simulation was proposed. In order to investigate the initial microstructure effect on the resulting microstructure and mechanical properties of partial austenitization Q and P steel, different initial microstructures were obtained by cooling process at different cooling rates before the Q and P process. The effect of initial microstructure on the mechanical properties of Q and P steel was systematically investigated via scanning electron microscopy (SEM), x-ray diffraction (XRD) and tensile test. The results showed that the modified QT selection method was more accurately than the traditional method in predicting the retained austenite volume fraction change trend. A fully matensite initial microstructure was apt to obtain a lamellar final microstructure, while an initial microstructure of ferrite and martensite resulted in a blocky final microstructure. Furthermore, the lamellar final microstructure had higher retained austenite stability and more comprehensive strength and ductility than the blocky final microstructure. (paper)