The research is supported by a Project Funded by the brand professional project form Yancheng teachers college (2016) and the teaching reform and practice of medicinal chemistry (2018YCTUJGY006) and the innovation and entrepreneurship training program for college students in jiangsu province ( 201910324016Z ) Abstract The content of ammonia nitrogen in water was determined by national standard method - nessler's reagent spectrophotometry. Through comparison, it was found that the method of reagent configuration, the amount of reagent, the detection wavelength, the color development time and the temperature had an impact on the analysis results in the ammonia nitrogen measurement in water by the reagent spectrophotometry. Based on the experimental results, the factors influencing the determination of ammonia nitrogen by spectrophotometry with nessler's reagent were discussed. Keywords Nessler's reagent spectrophotometry, Ammonia nitrogen, Influencing factors, Blank value, ABS value, Correlation coefficient. DOI : 10.7176/JEP/10-31-08 Publication date: November 30 th 2019