If a Constructed Infiltration Wetland Treatment System (CIW-TS) with reed beds for wastewater could regularly operate and get the desired treatment efficiency during cold winter, the system would realize all-year-round operation. The technology presented is the result of a pilot scale treatment system in Tianjin, north China, one that successfully operated for two years. A characteristic of the technology is that the system could regularly operate under ice layers when the average temperature was lower than −4°C. Wastewater percolates through the thick soil layer in a horizontal direction. Effluent quality is better than secondary treatment level, e.g. BOD5<20 mg/l, SS<20 mg/l, TN<15 mg/l, TP<0.6 mg/l. A yearly hydraulic loading rate of 14-20 m is appropriate.