Through field fixed location experiment and greenhouse incubation experiment, as well as a series of determinations of soil physical and chemical properties, the ameliorative effect and mechanism of three kinds of organic material on vertisol-the middle-low yield soil of Huaibei area have been explored.The results indicated that returning organic material to soil can increase soil porosity, reduce soil bulk density, improve soil perviousness and soil retention of water and fert ilizer, raise soil buffer capacity, supply multinutrients, and increase crops yields.The mechanism involved not only the reduction of shear stress of montmorillonite was reduced by humus, and restraint of its expansibility and shrinkage, but also supplying act ive organic colloid to form organo-mineral composite aggregate.In addition, organic acid can dissolve CaCO₃ in soil and release active Ca²⁺, which formed the bridge of composite aggregate, thereby, improved soil pedality etc.