Abstract: Nessler′s reagent spectrophotometry has the advantages of simple operation and high sensitivity in nitrogen measurement，so it has become a common method in water environmental monitoring. Studies were conducted on standard working solution measurement and experimental point distribution of calibration curve, cuvettes seclection and sample solution dilution in Water quality-Determination of ammonia nitrogen-Nessler′s reagent spectrophotometry (HJ 535-2009). The results show that: the measurement of standard nitrogen-ammonia solution is proper to select 5.00 mL graduated pipette to complete the total samples when drawing calibration curve, which can make operation times and workload appropriate and meet the requirements of HJ 535-2009 standard accuracy; the experimental point distribution on calibration curve or the option should not be arbitrary, otherwise it will affect the measurement accuracy; the 20 mm cuvette is favorable to reduce measurement error. If the concentration of measured sample is higher，it is better to choose single marking pipette more than 5.00 mL to dilute the solution; if the examination sample concentration is 0~100 μg /mL, there are 2 reasonable solution dilution schemes of 0，5，25，50 times and 0，2，10，50 times，and the two options are selecting 5.00，10.00，50 mL and 5.00，25.00，50.00 mL single marking pipette sampling dilution respectively.