Geochemical data distribution, especially the frequency distribution of trace elements, are positively deflective, and the calculation of the threshold is based on abnormal lognormal distribution. When qualitative analysis is conducted, the distributionof most of the sample is acceptable. But when quantitative analyzing lower limit of anomalies,the calculation must be in combination with the actual distribution of samples. This paper introduces the g-h distribution function to fit the sample data and ascertain the threshold according to the parameters. In combination with the sub-region median contrast filtering raised by Shi Changyi, the authors processed geochemical data of Gejiu and its peripheral areas and adjusted the size of the filter window by self-adapting, extracting the geochemical anomalies and delineating the targets.