Planosol is one of the major low yield upland soils in the Northeast part of China. The Aw horizon with 20 cm in depth beneath the topsoil in its solum has low aeration and water permeability, also low soil enzyme activity, that caused the topsoil suffer alternately excessive water and drought during the growing season, and its available layer for upland crops roots is only about 20 cm. Since 1980’s mechanical improvement Methods including subsoiler have been gradually developed as the major means for planosol improvement. To compare the effects of different mechanical improvement Methods on Planosol, three kinds of machines, namely the conventional subsoiler (CK), the stalk subsoil mixing plough (SSMP) and the subsoil interval mixing plough (SIMP) were operated in the large scale test field, in which the field operated by the conventional subsoiler functioned as control. After operation by the machines, soil physical properties and enzyme activities were investigated. Items of the soil physical properties include soil hardness, soil three phases and soil bulk density. Items of the soil enzyme activity include catalase, urease, intervase activities of the soils. The test fields were operated in the 853 farm, Heilongjiang province, and the indicator crop was soybean. The results showed that after operation by the SSMP and the SIMP, the soil hardness of the Aw horizon（albic horizon） was 7~9 kgf cm^-2 while the CK was 10~14 kg cm^-2. Their solid phase was 47.74 %、50.13 % respectively while the CK was 53.16 %，the soil bulk density of the both treatments was 14.01 %、10.19 % lower than the CK. Comparing with the CK, the SSMP and the SIMPtreatments deceased catalase activities of the soils, and the SSMP treatment deceased the urease, intervase activities of the Aw horizon, and increased the urease, intervase activities of the B horizon（argillic horizon, beneath the Aw horizon）. The two treatments increased soybean yield by 21.34 %，4.94 % respectively. The SSMP and the SIMP significantly improved the soil physical properties and the soil enzyme activity of Planosol. This research opened the new approach for the evaluation of the mechanical improvement for Planosol.