The invention relates to the technical field of lasers, and provides a DFB laser and a manufacturing method thereof. The manufacturing method comprises the steps of manufacturing a buffer layer, a lower limit layer, an active layer, an upper limiting layer, a corrosion stopping layer and a grating layer on a substrate, photoetching a ridge waveguide pattern including a rectangular part and a conical part when the ridge waveguide is etched, arranging the conical part on the light emitting surface side of the laser to be manufactured, wherein the conical top is flush with the light emitting surface, the conical bottom is connected with the rectangular part, and in the conical part, the width of the conical top is 0.3-0.5 micrometers smaller than the width of the conical bottom; synchronouslyetching the rectangular ridge waveguide and the conical ridge waveguide which correspond to the rectangular part and the conical part. The light with low wave length at the conical head is reflectedback to enter a cone bottom of a large light field limiting factor region, and the light with long wave length at the conical bottom is reflected back into the conical top of the small light field limiting factor region so as to be more easily emitted out. The conventional double-longitudinal mode is overcome, and the single-mode finished product rate of the laser can be effectively improved.