The cast thin section, scanning electronic microscope, cast image analysis and mercury injection analysis are applied to analyze the pore structure of the Sangonghe Formation reservoir in Baijiahai area. The main pore type of the Sangonghe Formation reservoir is secondary dissolved pore. The throat type is lamellar or curved lamellar and bundle tubular, mainly of moderate and fine throat. The Sangonghe Formation is mainly composed of typeⅠ-Ⅱ-Ⅲ reservoirs. The main influencing factors of the pore structure are sedimentation and diagenesis, and the cementation and dissolution are dominant factors.