Subsoil plays an important role as an important nutrient，water supply and source repository in plant growth.The role of subsoil improvement is to create more suitable soil conditions for crops.Subsoil improvement include deep digging，mixed layer subsoil tillage and subsoil fertility techniques，and it had the following characteristics:Firstly，subsoil improvement could increase crop yield.Super deep digging increased yield by 4.1%～35% on rotten soil，the mixed layer subsoil plow of first generation increased yield by 8%~16% on albic soil，the second generation increased yield by 10%～27%；Subsoil fertility increased yield by 17%～26%.Secondly，the effect of soil improvement was lasting long.The lasting effect of super deep digging on yield was 2～3 years on black rotten soil，and 10～15 years on special soil.The lasting effect of subsoil layer mixing plough and subsoil fertilizing on the yield was 7～10 years，and the effect of soil layer replacement was 3～5 years.Soil layer replacement was one of the “Semi permanent” soil improvement techniques.Thirdly，subsoil improvement needed special machine to carry out.Finally，subsoil improvement need to be invested too much money and the efficiency was relatively low，which restricted popularization and promotion of subsoil improved technology.