Abstract: Two types of B170P1 high-strength steel with thickness of 1.0 mm and 1.5 mm were welded with different laser welding process parameters. Welded joints were tested by metallographic examination and hardness measurement. The microstructure characteristics of the weld,base metal and heat-affected zone were analyzed. The mechanical properties of specimens welded under different laser welding parameters were investigated by tensile test. The results show that the amount of granular bainite in the weld increases with the increasing of welding power,and so the specimens have lower plasticity and ductility. Most of the grain boundary ferrite is stripy when the welding speed is large; otherwise,most of the grain boundary ferrite is massive. When heat input is low,the size of grain increases quickly with the increasing of heat input. The increasing of grain is controlled by adjusting heat input.