Based on analysis of chemical compositions of three crop straws(rice,wheat and rape),decomposition characteristics of straws and its effect on soil fertility in hilly area of Sichuan Basin was investigated through a fixed field experiment of two years.The results indicated that the soil was enriched with C,N,P,K when straw was returned to soil.The decomposition rate of straw in the first three months was faster than the later date.Decomposition rate(k) from the three straws followed the order as wheat straw > rice straw > rape straw,and straw-buried > straw-mulched.The content of nutrient releasing was characterized as K>P>N.Soil water retention curves of different treatments were derived,and the correlation coefficient of empirical equations were over 0.87.Straw mulched could improve soil granular structure,and increase the content of water-stable aggregates,so the ability of permeability,fertilizer and water conservation got improved.At the same time,the soil covered with straw was favorable to reducing soil bulk density and increasing soil porosity,soil organic matter,available N,available P and available K as well.So it realized the goal of soil fertility improvement.