Abstract: On the basis of the field outcrop and core observation,through the indoor sensitivity experiment,combining with the casting thin sections,physical properties testing,scanning electron microscopy(sem),mercury injection and other comprehensive analysis of a large number of test data,the study on the reservoir sensitivity characteristics and its formation mechanism was carried out.The study results show that He 8 reservoirs are of medium-to-weak velocity sensitivity,weak water sensitivity,weak acid sensitivity,salt sensitivity,medium-to-weak base sensitive characteristics.The formation of the sensitivity was not only affected by the type of clay minerals content of a reservoir and existing form,but also was associated with complex pore structure at the same time.