Based on the basis of observation data of box-beam temperature field, this study presented an comparative analysis of regulations on box-beam temperature gradient between China and foreign bridge engineering design, and proposed a new temperature difference distribution mode of concrete box beam along height of section. Finally, this study analyzed the external constraint temperature stress and temperature self-restrained stress of extra-long Longtan River bridge under different working conditions using ANSYS software, and compared them with measured results. This study provides reference for the measurement of sunshine temperature difference effect of box beam bridge.