Abstract: The high temperature tensile properties of 45 steel continuous casting billet at 600-1 350 ℃ were tested and analyzed by thermal simulation test machine, optical microscope, scanning electron microscope and energy spectrometer. The results show that the high temperature tensile strength of 45 steel continuously cast products decreased gradually with the increase of temperature. There were two kinds of brittle temperature zones, the first type was 1 200-1 350 ℃, and the second type was 600-900 ℃. The straightening temperature of 45 steel continuous casting products should be greater than 900 ℃ to prevent straightening cracks.