In this paper, we simulate y-ray energy deposition for different incident energies with four different models using the tool GEANT4 ( Geant4.7.0, 2005 ) developed by CERN (the Center of European Research of Nucleus).The results we obtained indicate that there are different peak values for different incident energies. That is, we can differentiate the incident energy accurately if the detector can determine the peak value accurately. This is meaningful for the geometrical configuration of the detector to get the most probable distribution (MPD) of energy deposition for different incident energies. According to the simulation, we can insert certain slices with large absorption coefficient to obtain a better MPD of energy deposition which will not alter the shape of the energy deposition.