Abstract: An uncertainty evaluation was established for evaluating the determination results of metoclopramide in pork by UPLC-MS/MS.According to the determination of metoclopramide residue in foodstuffs of animal origin for import and export-LC-MS/MS method ( SN/T 2227-2008) , the mathematical model of uncertainty was established and the sources of uncertainty were analyzed.As a result, the concentration of standard solution was the biggest factor for the uncertainty in measurement, the second was the repetition, the volume of sample was the smallest factor.The residue of metoclopramide in pork was 50.1 μg/kg, the expanded uncertainty was 5.0 μg/kg ( k = 2) .