By jointly solving the two-centre material equations and the coupled-wave equaions,we set up a dynamic model to study the time-space diffraction properties of the photorefractive volume holograms recorded by two colour light in doubly doped LiNbO3:Fe:Mn crystals.Numerical calculations show that,the time -space diffraction properties of the dynamic volume grating are relevant to the relative spatial phase shift between the index grating and the interference field.The spatial phase shift is defined between -π and π,the energy transferring direction between the two-coupled beams will be reversed with the reversion of the sign of the spatial phase shift.The winding of equal-phase line and the redistributed intensities of the two-coupled beams inside the crystal are given.