The invention discloses a Q345qENH weather-resistant bridge steel plate with the thickness smaller than or equal to 50 mm. The Q345qENH weather-resistant bridge steel plate comprises the chemical compositions including C, Si, Mn, P, S, Als, V, Ti, Cr, Ni, Nb, Cu, N, B, H and the balance Fe and residual elements. According to the Q345qENH weather-resistant bridge steel plate, the contents of elements such as B, N, H, Ti and S are controlled, so that the carbon equivalent and the crack sensitivity coefficient of the steel plate are greatly reduced, and the welding performance and the welding crack resistance of the steel plate are improved. The corrosion resistance index can be greatly increased, and the atmospheric corrosion resistance of the steel plate is improved. Phased control over theheating temperature and the heating time is beneficial to control over hot cracks, meanwhile, a billet is uniformly burned thoroughly, and deformation is facilitated. Matching of comprehensive properties such as tensile properties, low-temperature impact performance, cold bending performance and failure impact performance of the steel plate can be achieved. It is ensured that the shape of the steel plate is straight in the subsequent cutting process, and the plate shape problems such as rebound, warpage and distortion are not prone to being caused.