Abstract: In order to investigate the effects of high conveying pressure (20 MPa) and low conveying pressure (6.3 MPa) on bacterial corrosion of 20 steel. The uniform corrosion rate and pitting rate under different pressure conditions were evaluated through simulated corrosion loss tests under shale gas conditions. The morphology and composition of corrosion products were analyzed by focused ion beam (FIB) cutting and elemental composition analysis (EDS). Bacterial content and biofilm were measured by extinction dilution, 2D and 3D fluorescence methods to analyze the effect of pressure on bacterial activity. The results show that the uniform corrosion rate of 20 steel under high pressure and low pressure condition was lower than 0.03 mm/a, and the pitting rate was 0.18 mm/a and 0.21 mm/a, respectively. There were microorganisms and a small amount of S element on the surface of the corrosion products, indicating the corrosion action of sulfate reducing bacteria (SRB). The activity of bacteria under high pressure condition was lower than that under low pressure condition, but the biofilm was thicker and the bacteria were enriched in pitting pits, and the process of biofilm transferring corrosive electrons had been proved. In shale gas gathering and transportation environment, corrosion is mainly caused by SRB-induced pitting corrosion, while the activity of bacteria in high pressure environment is low, and its pitting ability and pitting rate are lower than that in low pressure environment.