Water quality change process of the estuary is effected not only by river runoff and emission flux, and is closely related to tidal cycles change. In order to find out the change process of water quality in estuary, based on a-day field investigation in May and August of 2009 in Shuangtaizi estuary, results show that the content of inorganic nitrogen is up to 2.75mg/L,and phosphate is 0.06 mg/L in May, while inorganic nitrogen is 1.28 mg/L, and phosphate is 0.05 mg/L in August. By analyzing the change process of water quality, the paper emphasize that the relation between the river runoff, tidal fluctuations change trend and change rule of water quality, thus provides some references for utilization and comprehensive management of the estuary water resource.
