We numerically investigate the impact of diffusion field in photovoltaic photorefractive crystals on the interaction between two coherent photovoltaic spatial solitons. Numerical simulations show that the in-phase interaction will result in the separation of the two solitons from each other, accompanied by the energy coupling between the beams, which is different from the case without diffusion field. And for the case of interaction out of phase, the two solitons are no longer the simply separated. Under certain conditions, they are exclusive to each other but deflect simultaneously to the same side.