A light source module includes a circuit board, a light-emitting diode, a lens, and a lamp screen. An upper surface of the lens has a first recessed portion including a flat surface and a curved side surface. The flat surface is at the center of the upper surface. The curved side surface surrounds the flat surface and stretches to the flat surface from a side surface of the lens to form the first recessed portion. A lower surface of the lens has a second recessed portion defining a recessed space and includes a curved surface and a sidewall portion. The curved surface is a convex surface and opposite to the flat surface. The sidewall portion surrounds the recessed space. An inner surface of the sidewall portion is concaved. The light-emitting diode is disposed in the recessed space. The lamp screen is used to diffuse the light passing through the lens.