Abstract: An auxiliary heat-dissipating device is provided, comprising: an expansion back plate having a plurality of vents and forming a respective slide on two vertical sides; a first shell positioned on the slide of the expansion back plate, the first shell has a first end opening and a second end opening, and the first end opening is aligned with the vents of the expansion back plate; a second shell having a first end opening and a second end opening, and the first end opening of the second shell will be inserted by the second end opening of the first shell; and a fan module provided within the first shell, the fan module will drive the wind flow between the vents of the expansion back plate and the second end opening of the second shell.