The influence of excessive inorganic nitrogen (NO3-, NH4+, NO2-) on the pH, inorganic carbon system and air-sea CO2 flux was studied in laboratory seawater simulation experiments. The result indicates that the excessive inorganic nitrogen significantly has an important influence on the inorganic carbon system in all conditions. At the NO3- addition groups, HCO3- and p (CO2) increase while pH and CO3(2-) decrease when the concentration of NO3- < or = 37.60 micromol x L(-1). But high concentrations > or = 188 micromol x L(-1) is just the reverse. The seawater changes from carbon source to carbon sink of atmospheric CO2 with NO3- addition increased. At the NH4+ addition groups, HCO3- and p (CO2) decrease while pH and CO3(2-) increase when the concentration of NH4+ < or = 25.20 micromol x L(-1). However, when the concentration of NH4+ > or = 126 micromol x L(-1), the concentrations of HCO3- and p (CO2) increase with NH4+ addition and the seawater changes from carbon sink to carbon source of atmospheric CO2 and the intensity of carbon source has a positive relationship with the concentration of NH4+. At the NO2- addition groups, the concentrations of HCO3- and p (CO2) decrease while pH and CO3(2-) increase with time scale and the seawater acts as a strong carbon sink with NO2- addition of 7.90 micromol x L(-1). While at the other NO2- concentration levels, the carbon sink is weak in seawater. The Chl-a concentration of nutrient addition groups compared with control (delta Chl-a) shows a significant negative correlation with delta p (CO2) (r = -0.87, p < 0.000 1, n = 16). The main controlling factor to the variation of inorganic carbon system is the adaptation of phytoplankton to different form and concentration of nitrogen.