Plugging structure of downcast tube well and construction method thereof

The invention provides a plugging structure of a downcast tube well and a construction method of the plugging structure. The plugging structure comprises finished waterproof concrete arranged in the downcast tube well and below the bottom plate part and a plugging assembly arranged on the bottom plate part. The top surface of the finished product waterproof concrete is not higher than the lower surface of the bottom plate part, and a gap of 5-8cm is reserved between the outer side surface of the finished product waterproof concrete and the inner wall of the downcast tube well; the plugging assembly comprises a rubber waterproof isolation layer, finished micro-expansive concrete and an annular water stop steel plate. Gaps among the finished waterproof concrete, the finished micro-expansive concrete and the downcast tube well are filled by grouting; a first water stop steel plate is fully welded at the position, 3-5 cm higher than the upper surface of the bottom plate part, of the downcast tube well. A large am