Abstract: In order to study the mixing relationship between seawater and surface water on the coast of Shenzhen,17 river water samples were collected near the estuary in the downstream of the Dasha river which disembogue into the sea. According to the hydrochemistry data,the relationships of major ions ( Ca 2+ 、Mg 2+ 、Na+、K+、SO 2-4、HCO-3) vs. Cl-,Br-vs. Cl-and the piper diagram were analyzed. The river water data in comparison with seawater dilution lines in the scatter diagrams are divided into four grou...