Experiments of high power laser welding of 1.8 mm thick galvanized steel B450LAD are performed by using a 15 kW CO2 laser. Four sets of welding process parameters are acquired through process optimization. The macrostructure and microstructure analysis, microhardness measurements and tensile tests have been done on these four welded joints. It is shown that sound welds can be achieved on 1.8 mm thick B450LAD steel at a laser power of 5.8～12.9 kW and a welding speed of 3～7 m/min. The weld section looks like an inverted trapezia and the heat affect zone (HAZ) is very narrow. Martensite structure is found in weld center and little martensite with more ferrite structure is observed in fine grained region . The hardness in weld center is 2 times as high as the base material. The welded joints show good tensile properties, and all tensile specimens are broken in the base material (BM). So these four groups of welding parameters can be used for guiding the actual high power laser welding of B450LAD at different applications.