A heat dissipation device is disposed in an electronic device. The electronic device has an opening and an upper wall and a lower wall at the position where the opening is formed. The heat dissipation device includes an air passage and a pair of air deflectors disposed on two opposite sides of the air passage. A distance between the pair of air deflectors is smaller than a distance between the upper wall and the lower wall. The pair of air deflectors is located between the upper wall and the lower wall. The hot air inside the electronic device after passing through the air passage will not be obstructed by a barrier but is directly discharged outside the electronic device through the opening.