Abstract: The effects of prestrain, aging temperature, aging time and solution carbon content on bake hardening property of the ultra-low-carbon bake hardening steel sheet were studied. The results show that the bake hardening value reduced because the free carbon atoms decreased with the increase of the deformation when the prestrain increased from 1% to 5%. As the increase of the aging temperature and aging time, the bake hardening value of the steel increased gradually because the carbon atom air mass saturation degree increased. The solution carbon content, which had no effect on Cottrell air mass saturation velocity and degree, had little effects on bake hardening.