An exemplary embodiment of a fan module includes fan units, and each fan unit includes a box-shaped shell, a guiding plate, and a torsion spring. The box-shaped shell includes a bottom plate and two opposite side walls substantially perpendicular to the bottom plate, and each side wall has a vent defined therein. The guiding plate is rotatable relative to the bottom plate of the shell. The torsion spring includes a first torsion arm, a second torsion arm, and a coil portion. The first torsion arm and the second torsion arm are urged against the bottom plate and the guiding plate respectively by torque force applied from the coil portion. Thereby, the guiding plate is driven to a position adjacent and generally parallel to one of the side walls to obstruct the corresponding vent by the second torsion arm.