Based Perchlorate is a new type of pollutant in drinkingwater, which is harmful to human health. The newly promulgated“Standards for Drinking Water Quality”(GB 5749-2022) has been listed asan expanded indicator. The uncertainty of determination of perchloratein drinking water by ion chromatography was evaluated, and the factorsaffecting the accuracy of the result were determined. On the StandardTest Method for Drinking Water Part 5: Inorganic Nonmetallic Indicators(GB/T 5750.5-2023), the perchlorate in drinking water was measured byion chromatography, and the uncertainty introduced in each step wasanalyzed and calculated. And evaluate its expanded uncertainty. Theperchlorate concentration in drinking water was ${0.101}\mathrm{{mg}}/\mathrm{L}$ and theextended uncertainty was ${0.005}\mathrm{{mg}}/\mathrm{L}\left({k =2}\right)$ . The measurement uncertainty is mainly introducedfrom six aspects, namely, the standard material itself, the preparationof standard working fluids, the preparation of series of standardworking fluids, the determination of sample repeatability, the recoveryrate and the main equipment. The most important factor affecting thetotal uncertainty is the uncertainty introduced in the preparationprocess of standard series working fluids.