Abstract: For high rockfill dams,the grain crushing in high stress field may raise the deformation rate of dam body and should be considered in numerical calculation.Because the traditional constitutive model for rockfill material can not reasonably reflect the effect of grain crushing,the calculated deformation of dam body is much different from the measured one.Based on the concept of binary medium model proposed by Professor Shen Zhujiang,a constitutive model of rockfill material considering grain crushing which was conceptualized as binary medium model consisting of structural system and breaking bond was presented,and the relationship between grain crushing rate and breaking parameter was established.An example of large scale triaxial test was taken to prove the rationality of the present model.