Abstract: The investigation on microstructure of rock is critical to the basic geology research in unconventional oil and gas reservoir, such as evolution, occurrence state of oil and gas, migration patterns and seepage characteristics. The advantages of pore structure characterization by computed tomography (CT) are multi-scale and without damage. The tar sand, tight sand and shale were scanned by the CT, and the results were compared between CT scan characterizations and normal measurements to show that the mineral total components are really close and the size distributions of mineral are overall small difference, and large difference in the mineral size less than 96 1m between CT scan and the sieving method on tar sand. The pore structure of tight sand was observed by the CT images. Due to the di erent measurements and sample size, the porosity tested by CT scan, is a little more. The layer structure of shale can be found by micro CT images, but the microstructure of pore are not distinguished by the micro CT. Compared with normal methods, the TOC and pyrite mineral are measured by the Nano CT scan, but the porosity test is smaller. It is due to the resolution of Nano CT is not high enough and the grey value between organic matter and pore are not easily separately.