Multilayer well casing

The present invention relates to a multilayer well casing. The multilayer well casing includes an outer tube, an inner tube, packed cartridges, a first blocking unit, a second blocking unit, a pump, a plurality of stripping plates and a gas introducing tube. A tube wall of the inner tube has screen areas, and a screen depth of every screen areas is not higher than a groundwater level. The packed cartridges are disposed between the outer tube and the inner tube. The first blocking unit and the second blocking unit are disposed in the inner tube, and a pumped area is defined between them. A disposed depth of the second blocking unit is lower than a disposed depth of the first blocking unit. An effluent hole of the pump is disposed in a top of the inner tube. Stripping plates are disposed between the effluent hole and the groundwater level. An introducing hole of the gas introducing tube is disposed between the groundwater level and the first blocking unit.