Abstract: Based on the field tests and the investigations, a three-stage subsoil mixing plough, as a result of the international cooperation of China and Japan, was developed. This plough could meet the need for the improvement of Planosol solum by mixing the second (Aw) and Third (B) horizons, while leaving the first (Ap) horizon undisturbed. The mean soil mixing rate, M_x was 0.7 and the mean transfer rate of the Aw to the B horizon, T_Aw→B was about 0.3. With the working width of 50 cm and the working depth of 60 cm, the total draught of the plough was about 30 kN under the normal field moisture condition. This draught requirement made the plough easily use in practice in China. In the field operated by the plough, good results for the soil physical properties were achieved. During the wet season, the excessive soil surface water could quickly penetrate into the subsoil. No recovery of soil hardness was observed after ploughing for four years, and hence the long term soil improvement was achieved. The yield increasing rate was 10%～27.9%, according to the large-scale extension tests.