A light source module is adapted to perform a light irradiation process on an object. The light source module includes a transparent cover, a reflector and a light emitting unit. The reflector covers the transparent cover, and the reflector and the transparent cover define a containing space. The light emitting unit is disposed inside the containing space. A perpendicular working distance from the transparent cover to the object is WD, a semi-minor axis of the reflector is A, and a semi-major axis of the reflector is B, wherein WD=2 A-3 to 3.5 A-3, and B=2 A to 2.5 A.