In order to analyze the accuracy and influencing factors of total phosphorus online analyzers, the quality control monitoring data of three different models of total phosphorus online analyzers in the provincial water quality automatic monitoring station of Luzhou City in 2023 is retrospectively analyzed. The results show that the total phosphorus online analyzer using ammonium molybdate spectrophotometry has high accuracy, stability, and linearity, but measurement deviations may occur periodically due to the influence of instrument reagent concentration and instrument calibration curve. The results of actual water sample recovery and laboratory comparison show that turbidity can affect the accuracy of analysis results, and instruments with turbidity compensation function are less affected by turbidity.