A vehicle washing system for a deep foundation pit narrow site comprises a water supply system, a high pressure pump system, a vehicle washing pond system, a three-level settling pond and a drainage ditch, wherein an annular support frame is arranged in a foundation pit, a concrete sealing plate is casted at the top of the annular support frame, the water supply system comprises a precipitation well, a submerged pump and a relaying water tank, and the high pressure pump system comprises a water storage tank, a boosting pump and a pressure pipeline. The vehicle washing system comprises a vehicle washing pond and a vehicle washing machine, wherein the vehicle washing pond is divided into an inward driving slope segment, a transition segment and an outward driving segment, the surfaces of theinward driving slope segment and the outward driving segment are double-gradient slop surfaces which enable vehicles to run up first and run down later, a bottom plate of the vehicle washing pond isa concrete sealing plate, the three-level settling pond is arranged on one side of the vehicle washing pond, and corresponding to the position of a retaining wall, a sand filtering port is formed in the retaining wall on one side of the vehicle washing pond, and muddy water in the vehicle washing pond flows into the three-level settling pond through the sand filtering port so as to settle. The vehicle washing system for the deep foundation pit narrow site solves the technical problems that a traditional vehicle washing system is large in occupied area, low in efficiency, small in water pressure and poor in cleaning effect, and wastes water resources.