It is important to maintain appropriate water quality of Saemangeum estuary lake and establish reasonal plans to manage water quality in order to develope Saemangeum project area successfully. To do these works, It is necessary to monitor water qualities in important places of Saemangeum lake and watershed. And It is also needed to apply water quality model which estimate water qualities of Seamangeum project area properly. It is necessary to come up with methods to manage water quality. And It is needed to appraise measures for persevering water quality by estimating water qualities using water quality model. It was resulted from analyzing water quality of Saemangeum estuary lake by three sluice gate open conditions, More widely do open sluice gates, better was the water quality. And It was estimated that scenario Ar-1, COD was 2.32㎎/L, TN was 0.73㎎/L and TP was 0.038㎎/L at the middle part of Mangyeong water area. And COD was 2.01㎎/L, TN was 0.59㎎/L and TP was 0.032㎎/L at the middle part of Dongjin water area. The water quality of the Dongjin water area was better than that of the Mangyeong water area.