Abstract: Studies of hydrocarbon geochemical exploration have been done in western Sichuan depression in conjugation with oil and gas exploration in Sichuan basin since `the Seventh Five Year Project', which have played an important role in the discovery of oil and gas in this area. Geological condition in western Sichuan depression is favorable for high concentration microseepage hydrocarbon enriched in soil which facilitates surface geochemical dectect. A typical large-scale gas field, namely Xinchang gas field is chosen as the study object for the relationship between characteristics of surface geochemical field and petroleum geology conditions. The results clearly indicate the surface hydrocarbon anomalies do exist and have certain link with deep reservoir, which is corresponding to local geological conditions of this area. A series of practical indicators are thus optimized for natural gas prospecting. Then, they are used to predict the zones with rich hydrocarbon accumulation and yield satisfactory gas-prospecting results, for example, some surface hydrocarbon anomalies are verified to be commercial oil and gas flows in boreholes. The studies mentioned above indicate hydrocarbon geochemical exploration technique has good application prospect in western Sichuan depression.