The utility model provides a cable lead-down tube rainproof casing tube which comprises a rainproof casing tube body which is sleeved outside a cable lead-down tube. The rainproof casing tube body is formed by the combination of two oppositely opened semi-tube bodies. One side of each of the two semi-tube bodies is connected through a hinge shaft, and the other side of each of the semi-tube bodies is provided with a concave and convex fitting edge. The two semi-tube bodies are embedded to form the tubular rainproof casing tube through the concave and convex fitting edges. According to the cable lead-down tube rainproof casing tube, two composable semi-tube bodies are embedded to form the cable lead-down tube rainproof casing tube with easy disassembly and assembly through the hinge shafts and the concave and convex fitting edges, a cable and a lead-down tube can be closely attached and fixed, and a good sealing effect can be achieved. The cable lead-down tube rainproof casing tube can be used for a long time, a phenomenon of loose sealing of a tube mouth can be avoided, the structure is simple, and the cable lead-down tube rainproof casing tube is convenient to install.