The uncertainty evaluation for determination of chloramphenicol residue in aquatic products by gas chromatography was carried out according to the method described in Evaluation and Expression of Uncertainty in Measurement (JJF.1059.1—2012）. Six aspects of measurement uncertainty were evaluated, including standard solution, weighing of sample, sample pretreatment, and the measurement repeatability of the equipment．The results showed that the measurement uncertainty was mainly due to sample pretreatment and standard curves, and in which the sample pretreatment was the biggest factor affecting uncertainty.