According to the evaluation of uncertainty in measurement theory, using graphite furnace atomic absorption spectrophotometric method for the determination of cadmium in crabs, for example, analyzes the sources of uncertainty of the entire testing process. Method GB/T 5009.15-2003 determination of cadmium in food for examination according to quantitative analysis of the content of cadmium in crabs, JJF 1059-1999 the evaluation and expression of uncertainty in measurement for evaluation based on a factor of uncertainty in measurement for evaluation and synthesis. Results Determination of cadmium in crabs by GFAAS can be expressed as wCd=(172±16) μg/kg, k=2.Conclusion By calculation, the expanded uncertainty is given for measurements of heavy metals by GFAAS provides a theoretical basis of quality control.