Abstract: The spectrophotometric determination method was adopted to analyze the measurement for the determination of total amount of free amino acids in tea.According to the relevant regulations documented in the《Evaluation and Expression of Uncertainty in Measurement》(JJF 1059.1-2012),the source of the uncertainty in the detection processwas identified,and the uncertainty calculation formula was deduced.Comparing the different effects of various factors on the measure results,it was found that the standard curve fitting had the biggest impact on the uncertainty.This finding made contribution to improving the quality of data measurement.