It is difficult to accurately interpret reservoir fluid with complex oil⁃water relation, by the conventional two⁃dimensional or three⁃dimensional geochemical chart, because of the fuzzy oil⁃bearing or water⁃bearing representation reflected by single two or three geochemical parameters. On the basis of geochemical data validated by oil production test, the geochemical pyrolysis parameters that directly reflect the distribution relationship of oil, gas and water in the reservoir are constructed. Four geochemical parameters are constructed and three two⁃dimensional subgraphs are constructed, which realize the comprehensive and comparison analysis of oil⁃bearing and water⁃bearing characteristic of samples. The final reservoir interpretation is obtained through the analysis of comprehensive geochemical cross chart united pyrolysis gas chromatography and geological fluorescence. The application of geochemical cross chart has achieved good effects in Agadem block, Niger.