Although high production oil has been achieved from continental shale of the Paleogene Hetaoyuan Formation by using large-scale hydraulic fracturing,less systematical research has been carried out on reservoir characteristics of the lacustrine shale in Biyang sag,Nanxiang Basin. In this paper,by use of thin sections and whole rock X-ray diffraction analyses,combining with the mineral composition feature of continental shale,the lacustrine shale oil in Biyang sag can be divided into massive mudstone,laminated argillaceous shale,laminated silty shale,laminated limestone shale and laminated dolomitic shale. With the photos taken by argon ion polishing high resolution scanning electron microscope(SEM),the reservoir characteristics in study area are concluded:(1)the main reservoir spaces include dissolution pore,intercrystal pore,intergranular pore,fracture,interlayer lamellation seam and macrostructure;(2)the pores are anisotropic;(3)mesopore is prior to micropore in study area,that is,the aperture size ranges from 0.841 to 213.34 nm with average in 4.76 nm, a main peak between 2 to 3nm and the second peak about 71 nm. It is indicated that rock type is the main factor controlling reservoir space development,and the corrosion pore,intercrystal pore,organic pore and interlayer lamellation seam are mainly developed in laminated limestone shale,which are beneficial to the shale oil accumulation.