Abstract: To develop Q500qENH bridge steel heavy plates meeting the requirements of high weather resistance and low yield ratio, this study conducted trial production using the production process of "low-carbon high-alloy composition + cooling process + tempering heat treatment". Through tensile, impact, and welding tests, combined with scanning electron microscopy and metallographic microscopy, the mechanical properties and microstructure of the steel plates after heat treatment were systematically analyzed.The results show that the microstructure of the tempered steel plates is mainly composed of bainite and acicular ferrite, and the fracture morphology presents ductile fracture. In addition, the transverse and longitudinal tensile properties and low-temperature impact properties of the steel plates are better than the standard requirements, with the ductile-brittle transition temperature ranging from -50 ℃ to -60 ℃, exhibiting low yield ratio, high weather resistance, and excellent low-temperature impact toughness. Meanwhile, the steel plates show excellent welding performance, and the mechanical properties of each region of the welded joints meet the technical standards.