Abstract: The sampling media in surface oil and gas geochemical exploration are dominated by near-surface soil and subsurface phreatic water,and snow cover is seldom used as the sampling media.An experimental study has been carried out over a known oil and gas reservoir in the Northwest China to investigate the content of the headspace hydrocarbons and the fluorescence intensity of the aromatics in the snow cover.The results show that the headspace methane(DC₁),the F360 and the F405 are effective in reflecting the existing oil and gas field,indicating that the snow-based geochemical exploration method has good application prospect in oil and gas exploration.The 3D fluorescence spectrum characteristics of both the snow cover and the surface soil are basically consistent within a certain area,suggesting that snow cover samples can be used to predict the reservoir fluid property.Compared with the surface soil,snow is "the guest from the sky",and the distribution of the hydrocarbons in the snow cover can be regarded as homogeneous,thus the background values of the hydrocarbons in the snow cover are basically homogeneous,without obvious differences from one sampling site to another.The snow cover,when developed to certain thickness,can act as the seal cap for the hydrocarbon gases migrated from the underlying layers.With its unique pores,cavities,and adsorption capability,the snow cover plays a role in adsorbing,accumulating and enriching the hydrocarbon gases migrated into the near-surface.The microbiological effect to the migrated hydrocarbons is minimized in the winter time,thus the disturbance factors of the geoche-mical anomaly obtained from the snow cover is relatively less,which provides a basis both for snow-based oil and gas geochemical exploration,and for the geochemical anomaly evaluation.