An electronic device includes an air dam module. The air dam module includes a frame defining a vent, a first rotating member, a second rotating member, and two third rotating members. The first rotating member is rotatably connected to a surface bounding the vent, to vertically block a lower half of the vent by its gravity. The second rotating member is rotatably connected to the surface bounding the vent. The third rotating members are rotatably connected to opposite ends of the second rotating member. The second and third rotating members vertically block an upper half of the vent by their gravities.