Abstract: High weather resistant steel Q350EWR1 is an important manufacturing material for railway locomotive and rolling stock bodies. The mechanical properties of its welded joints are crucial for the strength of the body and the service life of the locomotive. Handheld laser wire filling welding is a new welding process with strong welding adaptability. The quality of the high weather resistant steel Q350EWR1 handheld laser wire filling welding joint is of great significance for the innovation of vehicle manufacturing technology. This article uses 2.5mm and 4.0mm thick high weather resistant steel Q350EWR1 plates and handheld laser wire filling welding as carriers to conduct welding process, metallographic, hardness, tensile and fatigue tests on 2.5mm butt joints, 4.0mm butt joints and 2.5+4.0mm lap joints, and study the influence of handheld laser welding process on the mechanical properties of the above joints. The experimental results showed that a large amount of bainite appeared in the weld area, and the heat affected zones of the three types of joints were composed of fully and partially normalized zones. There was no coarse grain zone and the maximum width of the heat affected zone was only 1 mm; The weld zone has the highest hardness, followed by the heat affected zone, and the base metal has the lowest hardness; The tensile strength is not lower than that of the base material and the fracture location is located at the base material; The fatigue limits of 2.5mm butt joint, 4.0mm butt joint, and 2.5+4.0mm lap joint are 203MPa, 144MPa, and 91MPa, respectively.