This article discusses the patterns of NO effect on marine phytoplankton growth from chemical perspective.The experimental results of four algae, which are Platymonas halgolandica var.tsingtaoensis, Platymonas subcordiformis, Skeletonema costatum and Nitzschia closterium farma minutissima, are as follows: (i) In f/2 medium or f/50 medium, the growth of these four algae was obviously promoted or inhibited when nitric oxide of different concentrations was added once or twice each day during the cultivation; (ii) The NO effects on the growth of marine phytoplankton are in normal distribution.Different phytoplankton has different optimum NO concentration, which is consistent with the influence of NO on the growth of high plants; (iii) The effect of NO on Platymonas halgolandica var.tsingtaoensi, which is a food alga, is different from that on the red tide algae Skeletonema costatum and Nitzschia closterium farma minutissima.The authors put forward a new opinion that every alga has its own NO threshold concentration.All the above results may provide new clues to understand the formation of red tide.