Shale oil is revolutionizing the oil and gas energy in our country, and the resource potential of medium- and low- maturity shale oil is immense. In situ heating presents a promising technology for the effective development of these resources. This paper investigates the effects of conventional heating and microwave radiation heating on the organic- rich shale of the first Member of the Qingshankou Formation in the Songliao basin. We combined field emission scanning electron microscopy and low- temperature nitrogen adsorption experiments to systematically compare the pore structure and evolution characteristics of shale under microwave radiation and conventional heating. Our results show that the evolution of organic pores proceeds through three stages: pore opening, pore merging, and the formation of complex pores and fractures. Microwave radiation accelerates organic matter cracking at a given temperature, leading to the formation of organic pores and significantly promoting the development of micro- fractures. As temperature increases, pore structure parameters exhibit complex changes. Pore size initially increases and then decreases, whereas pore volume and specific surface area follow an increase- decrease- increase pattern. With prolonged microwave heating, the volume of pores smaller than 50 nm decreased significantly, while the volume of large pores increased substantially. This indicates that smaller pores gradually expand, merge, and evolve into larger pores. Microwave radiation demonstrates a more pronounced effect on enhancing shale pore space, resulting in more developed fractures, which are conducive to oil and gas seepage. However, excessively high microwave heating power and prolonged heating times can lead to pore destruction, hindering the improvement of shale microscopic pore space. This study provides valuable insights into the selection of in situ heating methods and the understanding of micro- porosity and fracture evolution during the heating process of medium- and low- maturity shale oil.