The invention discloses a lightweight fireproof energy-saving prefabricated exterior-wall hanging plate and a construction method thereof. The exterior-wall hanging plate comprises at least one wall plate, each wall plate comprises an inner-layer reinforced concrete plate, an outer-layer reinforced concrete plate, a thermal-insulation material layer and a heat-insulation connection bar; the thermal-insulation material layer is arranged between the inner-layer reinforced concrete plate and the outer-layer reinforced concrete plate; the thermal-insulation material layer comprises an organic thermal-insulation part and an inorganic thermal-insulation part surrounding the periphery of the organic thermal-insulation part, and the organic thermal-insulation part occupies most area of the thermal-insulation material layer; and the heat-insulation connection bar penetrates the thermal-insulation material layer, two ends of the heat-insulation connection bar are respectively fixedly connected with steel bars in the inner-layer reinforced concrete plate and the outer-layer reinforced concrete plate, and the heat-insulation connection bar is a steel bar with the exterior coated by engineering plastic. The disclosed lightweight fireproof energy-saving prefabricated exterior-wall hanging plate has the advantages of being lightweight and good in thermal-insulation performance, and is capable of avoiding potential safety hazard caused by flame and high-temperature flue gas entering the interior of the exterior-wall hanging plate via plate seams when a fire hazard happens.