The invention relates to a 
model method for calculating the 
fixed carbon content of ocean ultra-miniature 
phytoplankton. The method comprises the following steps: respectively testing abundance of 
synechococcus and ultra-miniature eukaryotic 
algae in an acquired sample; respectively calculating the carbon 
biomass and 
growth velocity of the 
synechococcus and the ultra-miniature eukaryotic 
algae so as to obtain the euphotic layer depth of sampling points of the 
synechococcus and the ultra-miniature eukaryotic 
algae; respectively calculating responses of the synechococcus and the ultra-miniature eukaryotic algae to surface 
light intensity on the basis of 
water depth variation; respectively calculating 
primary productivity of the synechococcus and the ultra-miniature eukaryotic algae so as to obtain 
primary productivity of ultra-miniature 
phytoplankton at the sampling points. By adopting the method, the 
fixed carbon content of ultra-miniature 
phytoplankton in offshore, shelf sea and high-
latitude open ocean (the 
latitude of which is greater than 40 degrees) can be calculated, compared with a method for determining the 
primary productivity of ultra-miniature phytoplankton on the basis of 14C in situ, the method saves time and labor, and can be used for estimating the primary 
conductivity of ultra-miniature phytoplankton in a relatively large research area. Tests show that the primary 
conductivity calculated by using the method has relatively good 
linear relationship with that of ultra-miniature phytoplankton tested on the basis of 14C, good 
estimation reliability is achieved, and a theoretic basis is provided for later practical study.