The utility model belongs to oilfield equipment, in particular to an intelligent type closed small-size movable water injection device suitable for the development of the oilfield ultra-low penetrating oil deposit water injection. The water injection device is characterized in that a closed water tank, a water injection pump, a water feeding pump, a filter, a frequency-conversion power distribution cabinet, a meter autocontrol cabinet, a medicine adding device, a pipe fitting, and a control valve are fixed on a cuboid sledge seat through foundation bolts respectively; the closed water tank is connected with the inlet of the water feeding pump; and the outlet of the water feeding pump is connected with the inlet of the filter through a pipeline; the outlet of the filter is connected with the inlet of the water injection pump; a water injection outlet of the water injection pump is connected with an outside-station water injection pipe network, and the inlet of the water injection pump and the outside-station water injection pipe network are connected with a manometer to measure pressure; the frequency-conversion power distribution cabinet is connected with a motor of the water injection pump and all the electric apparatus on a sledge through cables; and the meter autocontrol cabinet is connected with signal output ends of all the apparatus through cables. The intelligent type closed small-size movable water injection device has the advantages of short stage and easy moving, and meets the requirements of digital management, standardized design, and modularized construction.