In-situ conversion can transform organic matter in medium-low maturity shale into pyrolysis oil and gas, so as to realize effective reservoir development. During the process of in-situ conversion, the high pressure generated by pyrolysis oil and gas can destroy the pore structure of the reservoir and produce fractures, which affects the storage space and distribution characteristics of the fluid. It is significant to know the distribution characteristics of pore structure and the storage law of pyrolysis products for the development of medium-low maturity shale. Pyrolysis experiments at different temperatures were conducted to analyze the distribution of organic matter and pore structure of shale after pyrolysis by the nuclear magnetic resonance technology. In addition, the variation law of shale porosity was also clarified. The results show that pyrolysis can effectively improve the porosity properties of shale, and organic matter is mainly stored in the pore space of relaxation time at 0.1 ms. When the pyrolysis temperature is 400 ℃, the overall pore space size of shale is larger, which is more conducive to fluid migration and reservoir development.