The invention provides a horizontal subsurface flow constructed wetland reclaimed-water recycling system based on low-impact development circulating cooling water, and belongs to the technical field of ecological water treatment. The system consists of a water collection tank, an artificial wetland bed, a porous water distribution assembly, a cooling pipe assembly, a salt-resistant wetland plant,a multi-layer thermal insulation wetland filler, an activated carbon adsorption bed, and a water supply tank. The system is characterized in that the artificial wetland used has the functions of botha cooling system and a purification system, and when the system is placed on the roof of a large shopping mall or an industrial enterprise building, the artificial wetland can be used to continue cooling the cooling water and purifying the high salinity circulating cooling water, with rainwater as supplementary cooling water. The invention has a simple structure, and low construction and maintenance costs; long-term operation of the cooling system can be effectively maintained, achieving the goals of energy conservation, emission reduction, and reuse of reclaimed water; and the system can be widely used in the construction of urban low-impact development cooling water systems, and has broad development prospects.