The invention relates to a light and thin composite hot water heating floor which belongs to the technical field of heating. The floor structure comprises a ground decoration layer, an upper-layer metal heat-conducting layer, a heating pipe, a lower-layer metal heat-conducting layer, a calcium silicate board, a thermal insulation layer and a floor plate. The calcium silicate board can enhance pressure resistance, anti-aging deformation property and durability of the floor and enhance the heat conductivity in the heating pipe; a composite heat-conducting structure consists of the upper-layer metal heat-conducting layer, the heating layer coated with a metal film on the outer surface, the lower-layer metal heat-conducting layer and the calcium silicate board can effectively enhance the heat transfer of the floor structure layer, lead the ground temperature to be even, reduce the impacts of temperature stress and avoid the deformation and the damage of the floor; and the composite heat-conducting structure is combined with the thermal insulation layer therebelow, thereby being conductive to mounting and leveling and reducing the downward heat loss. The floor structure can simultaneously improve mechanical and thermal performances, be applicable to a variety of surface layers of wood floors, cement, tiles, stones and the like of newly built and existing buildings, solve the limitations of dry floor applications, avoid the shortcomings of the wet floor structure and realize strong adaptability, simple construction and convenient maintenance.