Abstract: The butt welding test of 6061 aluminum alloy plate with the thickness of 3 mm was carried out by using pulse-mode fiber laser. The effect of duty cycle on the weld formation, microstructure and properties of 6061 aluminum alloy joints was studied. The results show that with the duty cycle increasing, the weld width gradually increases. When the duty ratio is high, the proportion of equiaxed grains in the center of the fusion zone is relatively high and the size of the grain becomes bigger. This is due to the increase of the duty cycle, the duration of the peak power of the laser becomes longer in the single pulse period, that is, the time and intensity of the action of the laser beam on the liquid metal increase, and the heat input of the laser welding becomes bigger. The tensile strength of the joints is lower than that of the base material, and with the duty cycle increasing, the tensile strength gradually decreases. The fracture of the tensile specimens is located at the weld zone.