A water-cooled heat dissipation device for a notebook computer includes primarily a pad and a heat dissipation device at a bottom of the pad having an air through-hole. The heat dissipation structure has a fan below a U-shape plate, a groove of which is latched with parallel fins being transfixed with a metallic tube in a detouring way, with two ends of the metallic tube being connected to a water pump, allowing cooling water to circulate in the metallic tube to cool down the fins. The heat dissipation structure is fixed below the air through-hole of the pad with the two ends of the U-shape plate. In usage, a notebook computer is put on the pad, and temperature of the notebook computer is conducted to the pad. Furthermore, cold wind is blown to the pad by the fan, such that the notebook computer can be cooled down rapidly.