The invention discloses a water constructed wetland device and belongs to the technical field of constructed wetlands. The water constructed wetland device comprises a PVC frame; the PVC frame is provided with an aerated concrete block in an embedded manner; and an aquatic plant is planted on the aerated concrete block; an artificial medium filler is hung below the PVC frame. The invention also discloses a method of applying the water constructed wetland device to a water source protection land. For the device provided by the invention, by adopting an aerated concrete block planting layer, theporosity and the specific surface area of the aerated concrete block are high, and the aerated concrete block can adsorb and remove phosphorus in a water body and effectively increases the nitrogen and phosphorus removal rate as a bed body of microorganism growth and propagation. By adopting the method of applying the water constructed wetland device to the water source protection land, through triple synergistic effect of physics, chemistry and biology, the water quality of a water source is effectively improved, the removal rates of nitrogen and phosphorus pollutants can be increased, the alga growth is effectively controlled, and the water quality of the water source can also be improved.