The most common method for detecting the content of sorbic acid and benzoic acid in dairy products is the first method of high performance chromatography in GB 5009.28—2016 National Food Safety Standard for the Determination of Benzoic Acid, Sorbic Acid and Sodium Sacchar in Foods. When using high performance liquid chromatography for analysis, the pH value of the mobile phase has a great influence on the test results, especially on the retention and stability. Within a certain range, the smaller the pH value, the later the retention time, the more stable, and the smaller the peak offset, the larger pH value, the faster the retention time, the more unstable, and the larger the peak offset. The offset of the target peak has a significant impact on the qualitative quantitative determination of the results, so it is essential to obtain stable retention time and good peak shape for the experimental test results. This paper took the pH value in the phase as a variable, explored the influence law of the retention time and stability when its pH value was 7.0, 6.5, 6., 5.8, 5.5, 5.0, and found out the most suitable pH value of the mobile phase in the current laboratory environment to the detection quality.