Abstract: [Objective]To study the uncertainty evaluation of spectrophotometric determination of nitrite content in milk．[Method]The nitrite content in milk was determined by the second spectrophotometric method in the Determination of Nitrite and Nitrate in Food of National Food Safety Standard GB 5009.33-2016．By analyzing the source of the uncertainty，a complete mathematical model was established，and each component in the model was analyzed and evaluated．The relative standard uncertainty was synthesized，and the extended uncertainty of the synthetic relative standard uncertainty was obtained．[Result]When the confidence was 95%，the nitrite content of milk was X=（0.058±0.0034） mg/kg，k=2，and the extended uncertainty was U=0.0034 mg/kg．[Conclusion]The uncertainty of the test process mainly comes from the preparation process of standard working solution，the total volume of sample treatment liquid，the constant volume of test sample liquid and the repeatability of the sample．This method can provide a reference for the determination of the uncertainty of nitrite content in milk by spectrophotometry．

Key words: spectrophotometry, milk, nitrite, uncertainty