Abstract: In order to solve the problem of low strength of hot rolled coil of 14 mm thick 700L automobile beam steel,metallographic microscope and scanning electron microscope were used to analyze the microstructure and tensile fracture, and the effects of soaking temperature and time on the strength were studied. The results show that low soaking temperature or too long soaking time is the main reason for the unqualified strength of the test steel. The solid solution of niobium and titanium carbide is realized by optimizing the heating process of slab, the precipitation strengthening effect of niobium and titanium is brought into full play, and the problem of low strength is solved.