The low-alloy high-strength steel was welded by the laser wire filler welding, and the effects of laser power, wire feeding speed and defocus amount on the stability of the welding process were studied by high-speed camera, and a good welded joint was obtained with optimized process parameters. The results show that reducing the laser power or increasing the wire feed speed can reduce the porosity; When the defocus amount is 0 mm, the porosity is the lowest. The welding stability depends on the droplet transfer mode. When the droplet transfer mode is liquid bridge transfer, the welding stability of laser wire filling is improved. The wire melting zone of the laser wire filling welding joint is austenite and martensite dual-phase structure, and the laser action zone is a martensite single-phase structure. The microhardness of the laser zone is higher than that of the wire melting zone.