Abstract: This paper discussed the pore-throat characteristics of Lucaogou Formation, Permian, Jimusar Sag, by Miro-CT, FIB-SEM, N₂-Adsorption etc. The results indicated that Lucaogou Formation was tight oil reservoir with low to extra low permeability and its pores were falling into micro-nano scales and of various types, including intergranular pores, intercrystalline pores, dissolved pores, moldic pores, micro-fractures, interlayer fractures, and so on. The reservoir physical properties and pore structures were distinctive in different parts of Lucaogou Formation. Doloarenites in upper Tiandian have micro intergranular pores and dissolved pores. Calcareous siltstones in lower Tiandian formation held nano intergranular and intercrystalline pores with size of 0.05~0.1 μm. Calcareous ampelitic mustones in Feitiandian held intercrystalline pores, interlayer and micro fractures, size of fractures being 5~6 μm approximately.