In order to understand after construction cut-off wall of Dagu River downstream the influence of underground water level, and the water quality, on the basis of field investigation, observation and data collection, we use theory, mathematical statistics method, have a depth analysis on the shallow groundwater levels, water quality, temporal and spatial variation. The Dagu River downstream alluvial plain are water level low and buried shallow，present obvious seasonal rise or fall characteristics，2001 ~ 2011 years of research area of underground water level change relatively stable. It make the uplift in the upper reaches of the underground water level after Cut-off wall construction, make the change of groundwater natural runoff direction, remove the upper groundwater funnel. Until 2011, the Cl- content in groundwater of cutoff wall in the north side decreased significantly and the water quality became good, which explains that on the one hand the cutoff wall block the channel seawater intrusion, on the other hand the formed terrain conditions remains aquifers underground saltwater body washed cutoff wall in upstream.
