We record a reflection volume hologram with two plane waves in lithium niobate. By heating one corner of the LiNbO3 crystal, it will cause an inhomogeneous temperature distribution in the crystal. The thermal expansion results in small slight deformation of the volume hologram and then decreases the intensity of diffraction light. We also use the model of volume hologram being an integrator of the lights emitted from elementary light sources (VOHIL) to calculate the diffracted field for the linear thermal expansion. The results of experiment and simulation are both shown that the intensity of diffraction light decreases from the heating corner of the crystal. The change of intensity of diffraction light is predicted successfully with the model of VOHIL for the thermal expansion.