This research indicates that the trend of the distribution of inorganic nitrogen and N/P in the Bohai Sea are similar to that of the total phytoplankton in most months. The content of inorganic nitrogen in the coastal estuary waters is higher than that in the central region. The increment in ammonia-N content is relative to the activity of zooplankton. In winter, the maximum value of the nitrate-N/P is 7, and the transform of inorganic nitrogen is not sufficient. The content of inorganic nitrogen, which has certain effects on the reproduction of phytoplankton in this area, is lower that that of phosphate.