In order to realize the high power CO2 laser welding of 6061-T6 aluminum alloy sheet under high travel speed, filler wire ER4043 and ER5356 are selected for welding. In the experiments, welding hot cracking sensitivity is analyzed by use of fishbone samples, and optical microscope, scanning electron microscope, micro-hardness test and mechanical property test are applied to analyze the microstructure and properties of the joints. Results indicate that compared with filling wire ER5356, the hot crack sensibility of the joint welded with wire ER4043 is lower, and a maximal welding speed of 6 m/min can be reached. The weld contains columnar grains, equiaxes grains, and some dendrites grains. The weld has a micro-hardness of joint with ER4043 of 60~80 HV, a tensile strength of 240~262 MPa and a good bending property.