Abstract: For large size hot rolled H-beams with a web height H≥1 000 mm and a flange thickness h≥40 mm, the rolling load is relatively high in production and it is difficult to improve the product's microstructure and properties through traditional low-temperature and large reduction technology on existing production equipment. In order to achieve the localization of large size hot rolled H-beams, thermal simulation experiments, optical microscopes, scanning electron microscopes, transmission electron microscopes, tensile and impact tests were used to study the effect of rolling temperature on the microstructure and properties of Q420 grade HN1 109 mm×461 mm×21 mm×40.5 mm H-beam flanges. The results show that when the universal rolling temperature is reduced from1 000 ℃ to 900 ℃, the flange yield strength increases, the impact toughness first decreases and then increases, and the grain size is refined to a certain extent, the amount of V carbonitride precipitation increases, and its size gradually decreases. When the universal rolling temperature is controlled at 900 ℃ or 1 000 ℃, the microstructure and properties of Q420 grade large size hot rolled H-beam match well.