Abstract:Spectrophotometry was used to determine the uncertainty of nitrite contents in water. Ultraviolet spec－ trophotometry was adopted to determine the nitrite contents in water. Basic method and procedure measuring un－ certainty were also used to analyze various factors influencing the results. Mathematical model was established to calculate the uncertainty of nitrite contents. By analyzing and calculating the uncertainty components generated by purity of standard solution， standard stock solution allocation， dilution process of standard solution， curve fit－ ting process， dilution of unknown samples and sample measurement repeatability， it was found that the uncer－ tainty of nitrite contents in water was 0.485 mg/L and the uncertainty in measurement reached 0.017 mg/L（K=2）.