Heat dissipation device

A heat dissipation device positioned in a computer case, comprising:

• a fan received in the computer case and defining an air outlet facing the computer case;
• a plate positioned between an inner surface of the computer case and the fan, and slidable relative to the air outlet to open or close the air outlet;
• at least one motor fixed on two opposite sides of the fan, moving the plate relative to the air outlet;
• a motor driver installed into the computer case and electrically connected to the at least one motor, driving the at least one motor;
• a fan driver installed into the computer case and electrically connected to the fan, driving the fan;
• at least one temperature sensor installed into the computer case, sensing the temperature in the computer case;
• a controller electrically connected to the at least one temperature sensor, the motor driver, and the fan driver, wherein when the temperature detected by the at least one temperature sensor is higher than a preset threshold temperature, the controller signals the motor driver to activate the motor to move the plate from the air outlet and the fan driver to activate the fan to cool the computer case.