Abstract: China is not only a big agricultural but also a water-lacking country. Its irrigation water is lack far from enough. Moreover, the water is seriously polluted. The problem of irrigation water is solved not only by making good use of the existing water resources and developing the water-saving agriculture, but also by purifying the sewage and polluted water. This paper disscussed the mechanism and the feasilility of sewage purifization by ozone. Making full use of the recycled water will contribute much to ease off possible crisis of shortage of irrigation water.