Abstract: The-20℃ low temperature impact performance of 16 mm thick hot rolled coil plate of 700L automobile beam steel was not qualified. It was detected by optical microscope, scanning electron microscope and energy spectrometer. The reasons of nonconformity were analyzed. The results show that the coarse grains at the 1/2 thickness of the steel plate are the main cause of the unqualified low-temperature impact property at-20 ℃. By optimizing the temperature control range of the hot rolling process and increasing the thickness of the intermediate billet, the grains of the steel plate in the thickness direction are more uniform, and the stability of-20 ℃ low temperature impact performance is improved.