Abstract: Based on the results of large-scale loading plate tests of Shuibuya Dam,the Duncan-Chang E-B model parameters under two kinds of naturally graded rockfill materials,Qixia group limestone and Maokou group limestone,are studied by use of the back analysis method based on the IGA.The test results indicate that under the same loading path,the volumetric deformation and tangent modulus of naturally graded rockfill materials are larger than those of the scaled indoor triaxial tests,and there are distinct differences between them in mechanical property.Kur,obtained from the back analysis of the resilience modulus of naturally graded rockfill on Qixia group limestone,is approximately twice as K,however,nur is much larger than the elastic modulus index n proposed by Duncan.The researches on mechanical property of naturally graded coarse rockfill materials should be strengthened to provide a more reliable theoretical basis for the construction of super-high rockfill dams.