Bsaed on the requirements of "Standard examination methods for drinking water — Part 13: Radiological indices" (GB/T 5750.13—2023) as well as domestic and foreign uncertainty assessment guidelines, this paper presents the uncertainty evaluation of gross α and gross β analyses in actual water samples. By analyzing the uncertainty sources, combining various uncertainty components, and calculating the expanded uncertainty, the contribution of each uncertainty component to the total uncertainty was discussed. The analysis results for the water sample are gross α: (1.01±0.14) Bq/L (k=2), gross β: (0.60±0.09) Bq/L (k=2). The uncertainty sources mainly originated from the net counting rate, counting efficiency, and chemical recovery, which account for 52.3%，19.8%，and 20.0% in gross α , respectively, and 59.9%, 19.0%, and 13.6% in gross β, respectively.