Total phosphorus, as one of the main indicators for evaluating water eutrophication, is an important detection indicator for water quality monitoring in aquaculture processes. In order to determine the uncertainty of total phosphorus content in fishery water bodies, the total phosphorus content in fishery water bodies was measured according to GB 11893—1989 “Determination of total phosphorus in water quality-Ammonium molybdate spectrophotometric method”, and the measurement uncertainty of total phosphorus content was evaluated according to JJF 1059.1—2012 "Evaluation and Expression of Measurement Uncertainty". By establishing a measurement model, the main sources of uncertainty in the determination of total phosphorus by ammonium molybdate photometry can be divided into three categories: uncertainty introduced by repeated sample measurements The uncertainty introduced by the sample in the process of determining phosphorus content (including the standard uncertainty introduced by the phosphorus standard storage solution, the uncertainty introduced by the phosphorus standard solution preparation process, the uncertainty introduced by the total phosphorus standard curve testing point moving process, the uncertainty introduced by the total phosphorus standard curve fitting, and the uncertainty introduced by the detection instrument in determining the total phosphorus precision), as well as the uncertainty introduced by the sample in sampling, digestion The uncertainty introduced by the constant volume process. The expanded uncertainty of total phosphorus content in the sample can be expressed as: C=(0.19 ± 0.01) mg/L; k=2.[Chinese Fishery Quality and Standards,2024,14(3):08-15]