Lead is toxicological index of china's grain health standard and can be determined by atomic absorption spectrometry. According to GB / T27025- 2008《General requirements for the competence of testing and calibration laboratories,the testing laboratory should have and apply the procedure of estimation the uncertainty of the measurement. According to the technical requirements of JJF 1059—1999《Evaluation and expression of uncertainty in measurement》and CNAL / AG06《Measurement uncertainty policy implementation guide,the uncertainty of measurement in determination of the lead content of grain with the graphite furnace atomic absorption spectrometry were analyzed and the uncertainty evaluation results were obtained. These results help us to established the method of lead uncertainty analysis and provide scientific basis for the rationally evaluation of our laboratory detection results.