Abstract: Water conservancy construction sewage treatment mechanism, including a support mounting cylinder, where a variable-diameter sedimentation cylinder is arranged at one end of the support mounting cylinder, one half of the cylinder wall of the support mounting cylinder is a thin wall and the other half is a thick wall, and the thin wall and the thick wall are disposed oppositely. The water conservancy construction sewage treatment mechanism also includes: a variable-diameter diversion cylinder, which is arranged on the thin wall at the other end of the support mounting cylinder; several displacement diversion modules, which are arranged on the thick wall of the support mounting cylinder and include guide displacement structures and combined diversion structures; and a magnetic attraction displacement adjusting structure, which is arranged on the outer side of the thick wall of the support mounting cylinder and is matched with the guide displacement structures and the combined diversion structures.