The utility model relates to a deep-foundation-pit dewatering well-plugging device. In the prior art, after dewatering of well points is completed, a dewatering well can not be plugged easily, and the problem of secondary leakage is prone to occurrence. According to the technical scheme, the deep-foundation-pit dewatering well-plugging device comprises a steel plate base, a steel sleeve and water stop steel plates; the inner water stop steel plate is installed at the upper portion of the inner sleeve wall of the steel sleeve, the outer water stop steel plate is installed at the corresponding portion of the outer sleeve wall of the steel sleeve, the steel plate base is installed on the periphery of a lower opening of the sleeve wall of the steel sleeve, reinforcing steel bars are arranged at the portion, between the steel plate base and the outer water stop steel plate, of the outer sleeve wall of the steel sleeve at equal intervals, and a flange and a flange cover plate are installed on the inner water stop steel plate. The deep-foundation-pit dewatering well-plugging device is economical, applicable, reasonable, easy to machine, simple in technology, high in applicability, easy and convenient to install and use and good in construction effect; a large amount of engineering cost is saved, labor and material resources are saved, and the scheme is the innovation of deep-foundation-pit dewatering well-plugging devices.