The invention provides a backfilling construction method for a narrow area of a deep foundation pit. A supporting structure and a basement external wall arranged along the edge of a foundation pit arearranged in the foundation pit; a converting supporting plate is arranged between the supporting structure and the basement external wall; a plurality of discharging ports arranged along the edge ofthe foundation pit at intervals are formed in the converting supporting plate; and a backfilling area is formed among the supporting structure, the basement external wall and the bottom of the converting supporting plate. According to the method, due to the fact that backfilling and vibrating of vibrating rods are performed on the backfilling area below the discharging ports, and then, backfillingis continuously performed on the backfilling area in a multi-point manner so that backfilling of the backfilling area can be dense. The backfilling construction method for the narrow area of the deepfoundation pit solves the problems that when the operating distance between a foundation pit support and a building external wall is small, and manual tamping and mechanical grinding are inconvenientwhen a traditional method is adopted for foundation pit backfilling.