The uncertainty evaluation in the determination of inorganic arsenic in grain by liquid chromatography-atomic fluorescence spectrometry were evaluated to provide useful reference for establishing effective quality control methods. Based on the principle of uncertainty evaluation, the mathematical model of uncertainty was established and the source of each uncertainty component was analyzed, quantified and synthesized, and the uncertainty of measuring result was evaluated and described. The results showed that the main factors influencing the uncertainty included standard curve fitting of the least square method, and sample recovery rates. The inorganic arsenic content of the experimental determination result was （0.185±0.017） mg /kg．