Laser welding of B340LA high-strength steel is crucial for lightweight designing and manufacturing of automobiles. In this study, Fe30 metal powder was employed as a filler to perform B340LA high-strength steel laser powder filling welding, and the effect of the butt gap, welding speed, and powder feeding rate on weld quality was investigated. Furthermore, a high-quality weld with smooth weld morphology and better weld strength compared to base metal was obtained under optimized process parameters. Moreover, the butt gap was the most important process parameter affecting surface clearance and collapse, and the concave amount of the weld profile increased as the butt gap increased. However, when the butt gap was 0.15 mm, the weld collapsed. Welding speed had little effect on weld surface reinforcement and collapse. As the welding speed increased, the weld morphology became flat, and no collapse was observed. Furthermore, the powder feeding rate significantly influenced the tensile strength. As the powder feeding increased, the microstructure of the weldments was refined at a wide range, and the tensile strength increased. When the powder feeding rate was less than 8.27 g/min, the fracture of the welded joint occurred at the weld. However, when the powder feeding rate was ≥8.27 g/min, the welded joint broke at the base metal, and the strength of the welded joint was higher than that of the base metal. The research results enrich the basic theory of laser welding and provide technical support for B340LA high-strength steel laser welding of vehicles.