Based on characteristic analysis of different occurrence modes of percolated hydrocarbon gases in near-surface soil and combined with such geochemical indices over the known oil and gas accumulations as gas over the geological body, free hydrocarbon, heat released hydrocarbon and hydrocarbon by acidolysis, the authors hold that, although the test values of these indices over the same oil and gas accumulation show some differences in different periods, the anomaly range and variation trend of every index remain effective in indicating the information of deep oil and gas accumulation, and this reflects the effectiveness, reproducibility and stability of these indices. Therefore, the analysis of hydrocarbons of different modes of occurrence in near-surface soil can provide scientific basis for the effective utilization of oil and gas geochemical indices to the search of oil and gas accumulations.