The invention provides an OWT sewage processing system. The system comprises a buffer well with a water inlet pipe (A) and a water outlet pipe (A); a separation hydrolysis tank with a water inlet pipe(B) and a water outlet pipe (B); a water diversion tank with a water inlet pipe (C) and a water outlet pipe (C); a standard osmotic chamber with a water inlet pipe (D); and a water storage tank witha water inlet pipe (E). A biological pad, a seepage area, and a saturation area with a water outlet pipe (D) are arranged under the standard osmotic chamber in sequence. The buffer well is sequentially communicated with the separation hydrolysis tank, the water diversion tank, the standard osmotic chamber, and the water storage tank. The buffer well, the separation hydrolysis tank, the water diversion tank, the standard osmotic chamber, and the water storage tank are all arranged under a frozen soil layer. The opening of the water inlet pipe (A) is not higher than a sewage pipeline. All devices are arranged under the frozen soil layer, and thus thermal insulation facilities are not needed in winter. Sewage can go through each processing apparatus under the effect of self gravity, so the system does not need extra power, and a large amount of energy is saved. Moreover, the system does not need management. At the same time, sewage is subjected to an anaerobic treatment, an aerobic treatment, a physical and chemical treatment, a sterilization treatment, a phosphor removing treatment, and a de-nitrification treatment, and the sewage is converted into clean water.