A floor with a light steel structure and a construction method thereof, comprise a light steel framework and a concrete-poured surface layer; the light steel framework consists of dual-chord ladder beams intermittently arranged in transverse direction and reinforced punching and expanding nets arranged on the upper surface of the dual-chard ladder beams and connected with self-tapping screws; the concrete-poured surface layer is arranged on the upper surface of the reinforced punching and expanding nets; the dual-chard ladder beam consists of an upper chord rod, a lower chord rod and a cross arm that are fixedly connected with one another; the cross arm is connected on one side surface of the upper chord rod and the lower chord rod; the reinforced punching and expanding net is provided with V-shaped bars; hooks are densely arranged among the bars; and the V-shaped bars and the hooks are embedded in the concrete-poured surface layer. The floor has good heat-preservation and sound-insulation effect, does not vibrate when people walk on the floor, has no noise at the roof panel when raining, feels compact, completely overcomes the defects of the traditional preparation method, saves the formworks, has simple installation procedures, quick construction process, low cost, good anti-seismic performance, convenient arrangement for pipelines, and is suitable for low-rise, multi-rise or high-rise buildings.