The invention discloses a 500MPa-class weather-resistant bridge steel with impact power being not lower than 54J in a welded heat-affected zone at minus 40 DEG C. The weather-resistant bridge steel isprepared from the chemical components in percentage by weight: 0.04 to 0.08 percent of C, 0.20 to 0.40 percent of Si, 1.35 to 1.70 percent of Mn, 0.40 to 0.70 percent of Cr, 0.25 to 0.65 percent of Ni, 0.25 to 0.40 percent of Cu, 0.05 to 0.20 percent of Mo, 0.010 to 0.050 percent of Nb, 0.010 to 0.030 percent of V, 0.010 to 0.040 percent of Ti, 0.020 to 0.035 percent of Al, 0.0012 to 0.0050 percent of Ca, 0.0035 to 0.0080 percent of N, less than or equal to 0.0040 percent of O, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, and the balance Fe and inevitable impurities. According to the weather-resistant bridge steel provided by the invention, under the condition that the conventional electric-arc welding heat input ranges from 15 to 40Kj / cm, a structure of the welded heat-affected zone is formed by acicular ferrite, granular bainite and M-A components, so that the impact power of the welded heat-affected zone at minus 40 DEG C is not lower than 54J, the 500MPa-class weather-resistant bridge steel is weather-resistant and easy to weld, and the stable industrial production can be realized.