The work aims to analyze the cause of internal corrosion thinning of corner elbow used in a shale gas transformation platform, so as to determine the corrosion type and corrosion mechanism, put forward the anti-corrosion methods and improve the service safety of corner elbow. The corner elbow for shale gas transportation was taken as the research object to carry out basic research on corrosion thinning behavior in corner elbow, analyze corrosion morphology and distribution through macro observation and size measurement, explore the corrosion products through physical and chemical detection, micro observation and phase analysis, and comprehensively analyze the cause of corrosion thinning in corner elbow. Macroscopic analysis showed that there was a corrosion steps due to the sudden change in inner wall thickness between the outer arc side and the neutral zone, and the maximum thinning rate of wall thickness was 63.4%. The results of electron microscopy and metallographic analysis showed that the corrosion pits on the inner wall of the elbow developed in depth and peeled off layer by layer, and the corrosion products were loose with various morphologies. The results of energy spectrum and XRD analysis of the corrosion products showed that the corrosion products of the inner wall of the tube were mainly FeS, Fe2O3, FeCO3, etc. The internal corrosion might be related to CO2, H2S, SRB and so on. The synergistic action of sulfate reducing bacteria (SRB)-CO2 corrosion is the main reason for corrosion thinning of inner wall, while the existence of SRB catalyzes the CO2 corrosion. Meanwhile, the damage to corrosion product film and the erosion of elbow outside arc by Cl- accelerates the corrosion. It is suggested that the source of SRB be determined so as to effectively put fungicides in the pipeline. At the same time, the inner wall of the pipeline should be cleaned regularly to avoid long-term bacterial colonies attaching to the inner wall. In addition, a multi-stage gas-liquid separation device should be added to strictly control the moisture content in the gas phase.