Abstract: For shale reservoirs that are rich in organic matter, the porosity is one of the most key parameters for evaluation of oil and gas reserves, the existence of the organic pore make important contribution to the rock pore space, therefore, research on organic shale reservoir pore space is necessary. In this paper, taking the Longmaxi Formation shale reservoir of YY2 well in yongchuan block of South Sichuan as an example, the morphological characteristics and organic porosity of nanometer organic pores are analyzed and studied by combining the argon ion polishing scanning electron microscope data and image segmentation technology. The research shows that: The organic pores of the Longmaxi Formation in the YY2 well are relatively developed. The SEM images have large differences in the diameter of the organic pores. The SEM images of the six rock samples of the Longmaxi Formation are processed, and the obtained organic matter plane porosity is between 0.97% and 8.90%, and the aperture of some samples was small, and the plane porosity was below 1%. organic porosity calculated using the plane porosity and organic matter content which is in the range of 0.12%-0.75%, the average value is 0.39%, and accounts for 10.66% of the rock's porosity.