Abstract: In this paper we study the relations of distribution and composition of dissolved inorganic (DIN) with tidal change and other factors in spring of Quanzhou Bay. The result shows that Luoyang River inputted more NO^-₃-N from cropland aquaculture while Jinjiang River inputted more NH⁺₄-N from municipal sewage to the bay according to the nutrient content. The horizontal distribution of DIN was controlled both by NO^-₃-N and NH⁺₄-N. The average percentage of NH⁺₄-N reached 35%, so the composition of DIN didn’t balanced by the thermodynamic equilibrium in Quanzhou Bay. The relationships among different nitrogen species were affected by complicated nitrogen sources, human activities and biochemical processes according to the correlations between DIN and DO, COD. According to the linear regressions between DIN and salinity, the mixing behavior of NO^-₃-N and NO^-₂-N is suggested to be conservative besides some NH⁺₄-N from the fresh water end. Also, the mixing behaviors of DIN were controlled by both NO^-₃-N and NH⁺₄-N. DIN was also controlled by environmental factors such as suspended solids, temperature, salinity, pH and chl a. According to the distribution of DIN and its correlations with chl a, we suggest that the main source of NO^-₃-N is from human input. Tidal cycle variation of DIN at different stations were similar, both showed a decreasing trend during the tide rising due to the seawater dilution and an increasing trend during the tide falling. Moreover, the excess and annual increment of DIN concentrations was much serious in Quanzhou Bay where more attentions should be paid.