Abstract: The ammonium molybdate spectrophotometric method in GB 11893—89 could hardly satisfy the demand for rapid detection of low-content total phosphorus samples in large batches of Class I surface water, so the study mentioned by the title was proposed. 5 mL of water sample was taken and placed in a 15 mL-glass digestion tube, and 1.0 mL of a mixture of hydrochloric acid and nitric acid at a volume ratio of 3∶1 was added. The mixture was homogenized, placed in a rapid sealed vessel digestion instrument and digested at 160 ℃ for 10 min. After cooling, the mixture was made its volume up to 10 mL with water, shaken well, and filtered through a 0.45 μm aqueous filter membrane. The total phosphorus in the filtrate was determined by inductively coupled plasma tandem mass spectrometry in the oxygen reaction mode and focusing analysis mode, and germanium was selected as the internal standard for online calibration. As shown by the results, linear relationship between mass concentration of total phosphorus and signal intensity ratio of total phosphorus to the internal standard was kept in the range of 0.104‒1.01 mg·L⁻¹, with detection limit （3.143s） of 0.002 mg·L⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 97.3%‒109%, with RSDs （n=6） of the determined values in the range of 1.4%‒4.2%. This method was applied to the analysis of actual water samples, and the absolute values of the relative errors between the determined values and those obtained by GB 11893—89 were less than 3.0%.