Micro-pore type, pore distribution and structure characteristics of shale oil reservoir on Shahejie Fm. in Dongying Sag , Bohai Bay Basin, were studied by using a field-emission environmental scanning electron microscope, low-temperature nitrogen adsorption experiment and high-resolution quantitative analysis backscattered electron image. The results indicated that the matrix pores of Shahejie Fm. shale oil reservoir contain five types: inter-particle pores, intra-particle pores, inter-crystal pores, dissolved pores and intra-crystal pores. Favorable reservoir spaces of shale oil reservoirs are the pores in 100~3000nm diameter. Inter-particle pores, intra-particle pores and dissolved pores are predominant. The pore of mudstone and limestone contain the inkwell shape and the parallel-plate shape. Dolomite pore is mainly the parallel-plate shape and has best connectivity. Quantitative Plane Porosity and pore development of dolomite was larger than that of mudstone and Plane Porosity of mudstone was larger than that of limestone. Mineral composition and content, hydrocarbon discharge and hydrothermal process are believed the main factors to affect micro-pore characteristics. The clay minerals and clay-size particles are conductive to shale micro-pore development. Cementation and recrystallization of calcite are not conducive to pore development. Organic acid with hydrocarbon discharge and hydrothermal process are conductive to develop mineral secondary pores.