Abstract: The formula for calculating the characteristic values of geotechnical parameters specified in Code for Geotechnical Engineering Investigation (GB 50021) represents a classical statistical method for geotechnical investigation in China. However, the statistical method based on the T-distribution is limited in practical application. Additionally, the supplementary provisions of local geotechnical investigation standards have deficiencies, such as the absence of data distribution discrimination methods and the mismatch between standard deviation and assurance probability. Based on the statistical principle of the classical formula, this study analyzes the distribution types of geotechnical data as well as the applicable conditions and value determination methods of the characteristic value formula. An intuitive verification method for the approximate normal distribution of geotechnical data is established, and an outlier elimination method based on twice the standard deviation is proposed. The statistical mechanism of the variation coefficient greater than 0.3 is explained, and corresponding value determination suggestions are provided. This study effectively clarifies the statistical logic and applicable boundaries of geotechnical parameter characteristic values, and constructs a full-process technical framework covering geological unit division, outlier processing, distribution discrimination, and differentiated value determination of characteristic values.