Abstract: The distributions of the energy deposition of gamma-rays with various energies in LSO crystal were calculated by MCNP code and compared with the results of the experiment. The effects of different interactions between the ray and the material were analyzed. The laws of the energy deposition of gamma ray in axial and radial directions were obtained. In axial direction, the calculated distributions are approximately exponential for different incidental energies, and the deposited energy decreases a lot in the sub marginal region. In radial direction, the energy deposition in the region near the incident axis is mainly ascribed to cascade electrons, and it decreases as radius increases. In the region far from the incident axis, the deposited energy is mainly produced by the secondary gamma ra