A light source module adapted to a projecting device including a light bulb, a fan, and an air tunnel structure is provided. The fan is located by the light bulb for cooling the light bulb. The air tunnel structure is located respective to the location of the light bulb, for removing the heat generated by the light bulb. The air tunnel structure has a curved inner wall, a plurality of fins, and a tank. The curved inner wall is located inside the air tunnel structure respective to the location of the light bulb. The fins are formed on the curved inner wall for blocking the fragments generated by the explosion of the light bulb. The tank is located by a side of the curved inner wall for carrying the fragments clashing the fins.