Abstract: The main shaft of a screw conveyor fractured after one year of service. The cause of the main shaft fracture was analyzed by methods such as fracture morphology observation, chemical composition analysis, microstructure observation, and stress distribution simulation. The results show that the main shaft fractured at the root of the rotating body blade, and the mode of the fracture was multi-source corrosion fatigue failure. The stress concentration at the geometric mutation site at the blade root was the main cause of fatigue fracture. The corrosion effect in a strong acidic environment and the local stress concentration caused by transition geometric discontinuity defect of weld metal were the secondary causes that promoted the fracture of the main shaft. Under cyclic alternating stresses, cracks initiated and continuously expanded, eventually leading to the corrosion fatigue fracture of the main shaft. It was recommended to adopt arc transitions at both ends of the rotating body blades to alleviate stress concentration, and making the square discharge port to a rectangular blanking port with a larger aspect ratio to reduce material accumulation and lower the squeezing force on the main shaft.