Well shut-in after carbon dioxide fracturing is a key technology to enhance energy in tight sandstone reservoirs, and it can also extend existing fractures. In tight sandstone formations, weak plane (such as weak bedding and natural fractures) are widely distributed. CO2 can physically and chemically react with sandstone, which will affect the stability of the formation and the complexity of fractures. In this paper, the influence of CO2 on the fracture characteristics of sandstone with weak plane was investigated, and the materials were collected from the Ordos Basin with three weak plane angles (0°, 45° and 90°). Firstly, the specimens were divided into two groups, one was saturated with supercritical CO2 (SC-CO2) for 30 days, and the other was left in the air without any treatment. Then, the fracture toughness of corresponding specimens was tested through three-point bending tests, combined with acoustic emission technology to monitor the evolution of acoustic emission signals during the fracture process. It was found that: CO2 reaction with rock reduced the fracture toughness of tight sandstone specimens with weak plane by about 40%; CO2 reaction advanced the initial damage stage and increased the duration of the damage expansion stage; finally, the mechanism of CO2 influencing on the tight sandstone fracture toughness and fracture propagation with weak plane was discussed from the perspective of meso-damage mechanics. This study aims to improve the understanding of fracture behavior in tight sandstone reservoirs with weak plane during well shut-in after CO2 fracturing.