Abstract: Geochemical assessment of petroleum resource potential in a basin is one of the strategic problem,The study area is in Tuonamu region which is a promising area in the Qiangtang basin.This paper focuses on the surface geochemical exploration theories and methods in assessment of petroleum resource potential,We summarized some geochemical characters of preservation condition of petroleum.A new concept of structure energy coefficient in regional geochemical fields was put forward to calculate intension of composition differentiation in hydrocarbon migration.The GIS technique was used for predicting petroleum targets in study area.Our restdts show that surface geochemical exploration provides important geochemistry information in assessment of petroleum resource potential.