The invention provides a safe and economic double curtain wall borne by a building structure. The curtain wall comprises horizontal support plates (10) which extend along a supporting member of a window of an inner curtain wall in each layer in the building structure, wherein an outer curtain wall (20) is positioned and fixed on the upper surface of the horizontal support plate (10); an upper exhaust ventilation port (21) and a lower inlet ventilation port (22) are arranged above and under the outer curtain wall (20) respectively; and each layer is independent in space. The curtain wall saves materials on structure and connection, saves occupied space, high cost, complicated construction and fussy steel structure, improves the utilization area of the building, reduces the cost, shortens construction period, reduces long-term maintenance cost, has time and manpower saving, simple structure, low construction cost, high safety, convenient maintenance, low cost and the like, leads easy layer to circulate independently, reduces the problem of heat concentration on higher floor, and is integrated with sun-shading, heat insulating, sound insulating, warming, energy saving, heat preserving, dust proofing, mosquito and insect preventing, ventilating and other energy-saving environment-friendly functions in the whole system.