Abstract: On the basis of predecessors' research achievements,by making full use of core test and analysis data,the research on reservoir characteristics and controlling factors of Chang-8 member in Yanchang formation of Heqi-huanbei area in Ordos basin has been carried out.Results show that Chang-8 member mainly belongs to braided river delta sedimentary facie,which is of the gray,gray fine-grained sandstone,sandstone and inter-bedded with film of mudstone,silty mudstone and argillaceous siltstone.Partly contains a small amount of thin layer tuff and carbonaceous mudstone,with petrology characteristics of low compositional maturity and textural maturity.Reservoir is given priority to with residual original intergranular pore,secondary pore rare,and belongs to a typical low porosity low permeability reservoir.Reser-voir development is controlled by many factors,mainly including:the lithology,sedimentary facie and diagenetic factors.The lithology is the foundation,sedimentary is the condition and diagenesis is the key.Through the study on reservoir characteristics and controlling factors,the results provide geological basis for the exploration and development in the future.