The aluminum alloy, 5A06, was used in the experiment. High power Nd:YAG laser was adopted as the source and argon as shielding gas. The laser welding of Al alloy with thin plate was a difficult thing especially in the butt form of the thickness 0.5mm to 0.5mm and the fillet form of unequal thickness case. Blow hole and pore in the welding bead and deformation, usually, were the main defects. The welding parameters were tested and determined in the study. For the butt welding, the parameters of 1200W laser power with pulse mode and 1.8m/min welding rate were used for making a full penetration of weld bead and a smooth weld surface. The blow hole and pore were easily kept in weld bead when the power of 800W and 1500W was used. It was strongly depended on the pore tendency of Al-Mg alloy in the laser welding and the unstable welding process. For the fillet welding, the parameters of 1300W to approximately 1500W laser power with pulse mode, 1.8m/min welding rate, an angle of 15 degree between laser beam and vertical plane were used to get a high quality weld bead. In order to control the distortion of plate, a special method was designed and made for fixing the parts and keeping them in correct position. The experimental data showed that the best result was got when the copper cooling board was employed.