The invention relates to the technical field of 
water body nitrate pollution treatment and control, and is a method for culturing a denitrifying bacterium and using the bacterium to determine 
water body nitrate nitrogen isotopic composition. The method comprises the following steps of: (1) carrying out 
enrichment culture of the 
denitrifying bacteria, (2) detecting whether the 
denitrifying bacteria completely converse NO3- in a 
culture fluid, (3) concentrating of the 
denitrifying bacteria, (4) adding the concentrated 
cell culture to a sample 
bottle, purifying an upper space and removing N2O in the denitrifying bacterium liquid, (5) conversing NO3- in the sample to N2O, (6) determining the N2O 
nitrogen isotope, and (7) correcting the 
nitrogen isotope determination result to complete the test. The positive effects of the invention are as follows: the culture of the denitrifying 
bacteria can be completed by using only a common 
saline bottle or a triangular flask, the detection of 
sulfanilamide color development improves the reliability of the determination result, and the determination cost is reduced. For the current situation that severe 
water body nitrate pollution is urgently needed to be treated, the method of the invention has the advantages of scientificalness, simplicity, and high maneuverability, and has a broad popularization prospect.