Objective: To improve the accuracy of the results of cadmium (Cd) content in kelp (Laminaria japonica) by graphite furnace atomic absorption spectrometry (GF-AAS). Methods: The concentration of Cd element in kelp sample was measured by using GF-AAS after microwave digestion according to the standard of GB 5009.15—2014. Combining with the experimental process and mathematical model, the possible sources of measurement uncertainty were firstly identified, then the components of each standard uncertainties were calculated, and finally each parameter of uncertainties was synthesized, and the whole uncertainty was evaluated. Results: when the value of Cd concentration in kelp was 0.202 mg/kg, the expanded uncertainty was 0.008 mg/kg (k=2). Conclusion: The uncertainty of the method is mainly derived from the determination of Cd concentration in the sample solution, which is basically introduced by standard working solution preparation. Moreover, the uncertainty caused by the sample recovery rate is also large. So the quality control of the parameter of uncertainties should be strengthened in the future.