Abstract： Objective To improve the accuracy of high performance liquid chromatography(HPLC)results for the determination of related substances impurity Ⅰ in nifedipine,and to identify the key influencing factors in the test process.Methods According to the method of Chinese pharmacopoeia(2020 edition)nifedipine related substances determination results,the influencing factors were listed and the quantitative model was established,according to JJF 1059.1-2012"Evaluation and Expression of Measurement Uncertainty",the combined uncertainty U and expanded uncertainty U were calculated.Results When the inclusion factor k=2 and the confidence probability was 95％,the expanded uncertainty of high-performance liquid chromatography determination of nifedipine-related substance impurity Ⅰ was 0.002％,and the measurement result was expressed as(0.04±0.002)％.Conclusion Due to the low content of impurity Ⅰ,the uncertainty of HPLC determination of nifedipine impurity Ⅰ mainly comes from the repeatability of random factor samples.