Vertical migration of hydrocarbon in underground oil and gas accumulation and its ring halo effect have been demonstrated is many oil and gas fields. On such a basis, oil and gas geochemical exploration methods with multi-indices and multi-parameters have been widely used in practical work. Nevertheless, the effects of geochemical exploration have not been always satisfactory, which may be attibuted mainly to the inadequate consideration of such factors as the complexity of natural conditions at surface, the diversity of oil and gas trap types and the diversity of geochemical anomaly patterns. In the past, good geochemical exploration results seemed quite easily obtained in areas where geological and surface geochemical conditions were comparatively simple, whereas it was rather difficult to gain achievements under complex conditions. Based on some examples of oil and gas geochemical exploration conducted by the authors in recent years,the present paper has summarized the methods for eliminating such interference factors as surface Indscape and media as well as the problems of discriminatiog ring halo anomalies from top anomalies.