The invention discloses an environment-friendly sanitary sewer which comprises a cast iron pipe with the inner wall evenly coated with a paraffin layer. A preparation method of the sanitary sewer includes the steps that A, a pipe mold is mounted on a metal centrifuge, and high-temperature molten iron is continuously injected into the pipe mold, so that a pipe blank is formed; B, the pipe blank istaken out after being solidified and cooled, the two ends of the pipe blank are sealed, enough molten paraffin is poured from one end, and then the pipe blank is transversely arranged with the axis being horizontal and is rotated by at least one circle; C, the pipe blank is rotated until the axis is vertical, the lower port is opened, and excessive paraffin flows out totally; and D, the paraffin is cooled to the room temperature, so that the sanitary sewer is obtained. The invention further discloses an installation method of the sanitary sewer. The environment-friendly sanitary sewer and thepreparation and installation methods thereof have the beneficial effects that on the premise that corrosion resistance of the cast iron pipe is ensured, the environment protection requirement of usedpipelines after manufacturing, machining, coating, disassembling and updating is met, and no harm exists in the whole process.