Abstract: Planosol is one of the main agricultural soils in the northeast of China, concentrates in Heilongjiang and Jilin provinces relatively. Its total area is approximately 3.312 million hm2 in Heilongjiang Province, centrally distributed in the Sanjiang Plain, its cultivated land area is about 0.88 million hm2, accounting for 25.4% of the total arable land in the area. The subsoil of planosol often presents the physical and chemical characteristics of “hard, board and thin” during the growing period of crops, which results in serious drought and water logging. According to the characteristics of the two-layer nature of the planosol in its mechanical composition, we proposed a new soil modification route to treat the “sand” of the Aw (planosol layer) horizon with the “clay” of the B horizon (illuvia horizon), clarified the principle of “the Ap horizon in depth of 20 cm undisturbed, while mix the subsoil in depth of 30-40 cm”, and developed a three-stage subsoil mixing plough which could mixed the Aw horizon and the horizon with the ratio of 1:1 under the condition of the black soil layer position unchanged, improved the permeability and the water storage capability of the subsoil. After many years experiment and demonstration, the whole subsoil layer mixed, seriously affect the mechanical seeding. In order to improve the soil modification efficiency, form suitable soil structure and improve barren subsoil, the subsoil interval mixing plough was designed on the basis of the three-stage subsoil mixing plough, which could plough the Ap horizon in depth of 20 cm undisturbed, mix the subsoil in depth of 30cm below, separate 62 cm without mixing. We conducted field experiment in the 854 state farm during 2016-2017, and investigated the physical and chemical characteristics of soil and the agronomic traits and yield of soybean of subsoil interval mixing area and surface ploughing and deep digging area to definite the yield-increasing mechanism of the interval subsoil mixing plough The result showed that compared with surface ploughing and deep digging area two years after soil modification, the subsoil interval mixing area improved the physical characteristics of the subsoil, during 20-40 cm soil layer, the soil water content increased by 2.13-3.20 percentage point, the hardness reduced by 40%-50%，and there was no peak; improved the soil permeability, the solid phase decreased by 5.06 percentage point, the liquid phase increased by 3.17 percentage point, and the gas phase increased by 1.89 percentage point; improved nutrient content of subsoil, the available nitrogen increased by 33.77%, the available phosphorus increased by 39.25%, the available potassium increased by 4.16% and the organic matter increased by15.85%, improved the total nutrients content of subsoil and alleviated soil acidity meanwhile. The yield of soybean in two years increased by 12.66%-13.28% compared with the CK area, the soil modification effect last long at a time, significant increase in production. The results could provide technical support for improving planosol and the same low yield soil and promoting high crop yields.