Abstract: The charactors of dilatancy of sands and the concept of the state parameter were discussed.By means of the comparative analysis of experimental results,the concept of phase trans formation line was established.Phase transformation void ratio and phase transformation stress ratio were put forward.State parameter computing formula and a specific method for differentiating sands dilatancy according to state parameter were posed.A kind of method for computing sands dilatancy ratio was established.All of these research would help to provide foundation for creating sannds constitutive model.