Simulated study in green horse on the effect of applied rates and methods of organic materials on soil structure was conducted for 4 years. The organic materials used in eaperiment were dry rice straw+dry milk vetch, rice straw, milk vetch and waterlogged compost of rice straw. Same physical conditions during the period of incubation were controlled. Results showed that the soil structure and porosity were markedly improved and the rupture modulus of soil core were decreased by application of organic materials in clayey soil. The stability of soil aggregates was positively correlated with the content of organic matter, heavy fractional organic matter, amorphous iron oxide and activity of iron oxides (Fe_n/Fe_t),while the rupture modulus of soil core were negatively correlated with the parameters mentioned above. It sees that the amorphous iron oxide may be used as an indirect index for the evaluation of high yield paddy soils with good structure. The macropore apace of the soils applying organic materials was increased significantly during the dehydration of soil, which is beneficial for the growth of upland crops on clayey paddy soils after harvest of rice. The effect of direct application of rice straw on the improvement of soil structure was much better than that of application of waterlogged compost of rice straw or mixed application of rice straw and milk vetch. Therefore, it is necessary to apply a certain quantity of rice straw for the improvement of soil structure, while sowing area of green manure crops are reduced recently.