The invention discloses a foundation pit support and water stop integrated structure and a construction method thereof. The foundation pit support and water stop integrated structure comprises a concrete wall, wherein the concrete wall is arranged under the ground of the periphery of a foundation pit, and a plurality of cylindrical reinforcement cages are vertically arranged in the concrete wall. The construction method of the foundation pit support and water stop integrated structure is characterized by comprising the following steps of excavating a guide channel, casting a guide wall, forming a channel in the channel section, arranging the reinforcement cages, casting concrete, and the like. The foundation pit support and water stop integrated structure and the construction method have the characteristics that the rigidity of an underground continuous wall is large, and the water stop effect is good; the installation of the reinforcement cages of a row pile support structure is convenient and rapid, the technology difficulty is low, the construction is rapid, the quality can be easily controlled, and the foundation pit support and water stop integrated structure is especially suitable for water-rich sandy gravel ground layers.