The uncertainty in the measurement for determination of the total sugar, reducing sugar, chlorine, potassium in tobacco by the continuous flow method was evaluated with the actual instance. The influence factors on the uncertainty in the measurement for determination of total sugar, reducing sugar, chlorine, potassium content were analyzed, the component and combined uncertainties were calculated, and the expanded uncertainties of the above three components were 0.44%, 0.40%, 0.02% and 0.06%, respectively, which providing the credibility and confidence interval to the measurement results.