The principle of recording and reconstructing volume gratings with front phase encoding was expounded. The diffraction selectivity of superimposed volume gratings,utilizing the coupled wave theory,is deduced from the first order differential equation of diffracted wave. A complex stochastic process function is proposed,with whose correlation function,the necessary and sufficient condition of random wave front phase encoding volume gratings reconstructing without crosstalk is obtained. A diffraction selectivity theoretical analysis method of volume gratings with wave front phase encoding is proposed.