Deep foundation pit engineering under complex environmental conditions in urban areas often involves complex confined water treatment problems. When the confined aquifer is relatively deep and only the scheme of hanging curtain combined with pit decompression water can be adopted, it is necessary to assess the impact of confined water precipitation on surrounding environment. And one of the key problem is to determine reasonable hydrogeological parameters. Based on a deep excavation project located in the Yangtze River floodplain geomorphic unit, a field pumping test of multiple wells was carried out for its thick confined aquifer. The preliminary hydrogeological parameters were given according to the analytical method of single well pumping test. On this basis, a numerical analysis model of groundwater seepage for multiple well pumping test was established, and reasonable hydrogeological parameters were determined based on back analysis. It provided a direct basis for analyzing the impact of confined water dewatering on the surrounding environment.