Abstract: In order to compare the differences between laser MAG composite welding and MAG welding rocesses for Q345NQR2 weathering steel, this article uses qualified welded joints made of 10mm thick 345NQR2 weathering steel after butt welding to conduct comparative analysis from three aspects: weld morphology, metallographic structure, and mechanical properties. The results showed that laser MAG composite welding achieved high efficiency and strength through "deep narrow weld+martensitic strengthening", with an average hardness value of 268 HV in the heat affected zone weld. Microcracks appeared on the surface when the bending angle reached 180°, and the tensile test broke at the base metal, indicating that the strength of the welded joint was higher than that of the base metal. MAG ensures safety and stability by virtue of "wide and shallow weld+ferrite toughness". The weld hardness range is 202-286 HV, and the peak hardness of the heat affected zone reaches 228 HV. The tensile test fracture positions of welded joints are in the heat affected zone, and the fracture is mostly cut in the 45° direction. When the bending angle of the bending sample is 180°, there is no crack in the bending Lamian Noodles, and the welds show good plasticity and weldability.