Abstract: To study the main factors influencing the hole expansion property of FB780 advanced high strength steel, hole expanding tests were carried out according to Chinese standard GB/T 15825.4-2008. The microstructures of the tested steel before and after hole expansion, morphology of burnish zone and fracture zone on the punching surface, hardness profile of the micro-area within 2 mm distance near punch holes, morphology and second phase in the position of the through-wall cracks on the specimens were studied with the help of optical microscope, scanning electron microscope, and micro-hardness tester, etc. The key factors influencing hole expansion property were obtained. The results reveal that key factors influencing hole expansion property of FB780 steel included hardness and microstructure of micro-area near punch hole and quality of punch holes surface. It is found that the hole expansion ratio decreased with the significant increase of hardness of the micro-area near punch holes. Crack's formation and expansion were conducted by microporous gathered mode during hole expansion process. The improvement of microstructure and punching quality was good for hole expansion property.