Abstract: An integrated laser cutting and welding optical system with flat distribution of laser energy and adjustable spot size was designed in order to improve the quality of cutting and welding plates with different thicknesses. The influence of sub-lens aperture and focal length on spot uniformity of microlens array was analyzed by simulation. A microlens array was designed to transform the multi-mode laser beam into a square spot with a flat-top energy distribution. Based on the principle of optical compensation, the relation between the zoom ratio and the moving distance of the lenses was deduced, and the optical compensation zoom optical system was designed. The design results show that the microlens array combined with the zoom optical system can achieve the cutting spot size of 0.5 mm×0.5 mm, 0.75 mm×0.75 mm, 1 mm×1 mm three variable, with zero drift of image plane and spot uniformity greater than 88.80%. When the scanning angle of the digital galvanometer is ±1.44°, the maximum welding range is 0~6 mm, and the spot uniformity of the welding edge is greater than 87.72%. The function of smoothing light and changing spots is successfully realized to meet the needs of cutting and welding in different application scenes.