A heat dissipating device is provided. The heat dissipating device includes at least one fan, a temperature detecting unit, a fan control unit, and a power consumption control unit. The temperature detecting unit detects a temperature inside the host. The fan control unit controls the rotating speed of the fan. The power consumption control unit calculates the total power consumption of the host, and outputs a control signal to the fan control unit according to the temperature inside the host and the total power consumption of the host, so as to adjust the rotating speed of the fan.