By taking into account of diffusion, drift and the photovoltaic effect, the band transport equations are set up when the volume holography is recorded in doubly doped LiNbO 3crystals by using two color lights, and obtain the analytical solution of the steady state space charge field. The effects of the ratio of intensities of two color lights, the grating wave vector, the doubly doped concentrations and the oxidation reduction state on the steady state space charge field are calculated and discussed.