Abstract: In order to compare the differences between bottom-up and top-down methods for evaluating uncertainty in measurement, the laboratory data concerning quality control were used for assessing uncertainties in measurement of potassium in tobacco with bottom-up method and the quality control chart and robust statistics-iterative method in top-down method separately.The results showed that: 1) The expanding uncertainty was 0.034% for the quality control chart and robust statistics-iterative method, and that for bottom-up method was 0.048%, the two methods presented good consistency. 2) Top-down method could reflect long term measurement level of a laboratory, it was suitable for interior quality control within a laboratory where a large number of quality control data had been accumulated.