Abstract: Dual phase steel with 63.8% of ferrite grains and 53% of martensite grains in the size distribution of 0.5 to 1 μm was produced through adopting the initial microstructure of ferrite,bainite and martensite in combination with the cold rolling and continuous annealing process.The grain refining mechanism of vanadium-containing dual phase steel based on the initial microstructure of ferrite,martensite and bainite was investigated.It is found that the refining theory mainly has three aspects:(1) microstructure refinement by deformation including hot rolling and cold rolling for the initial microstructure of ferrite,martensite and bainite;(2) recrystallization and rapid austenitization of the as-cold rolled microstructure;and(3) vanadium precipitation preventing austenite from growing up.