The deep foundation pit engineering with superthick unconfined aquifer near the river always has problems such as strong permeability of stratum, large water inflow and difficulty in dewatering. The influence of different diaphragm wall depths and deep horizontal bottom sealing effect on water inflow and drawdown outside the foundation pit of Juyuanzhou Station of Fuzhou Metro Line 2 is studied by combination of theoretical analysis and threedimensional numerical simulation method; and the optimum embedded depth of diaphragm wall and the location and thickness of deep horizontal bottom sealing are determined. The engineering practice shows that: (1) The actual sealing effect of deep horizontal bottom sealing is over 93% on average and the water inflow is reduced by 75%, which effectively reduces the difficulty of dewatering and ensures the safe and smooth completion of the foundation pit project. (2) Based on the suspended water curtain for cutting off drains, the horizontal bottom sealing curtain can effectively reduce the vertical permeability of the bottom stratum and the water inflow of the foundation pit with superthick sand and pebble layer. (3) The position of horizontal bottom sealing should meet the requirements of antiinrushing, and a certain space should be reserved at the upper part so as to arrange drainage well filters to drain groundwater leaking from the bottom sealing to the pit.