With single pump beam incident in CeKNSBN, the temporal evolution of transmission intensity of pumping beam in CeKNSBN crystal is experimentally studied by altering the angle φ between the polarizing orientation of the pump beam and c axis of the crystal. The experiment is carried out on crystal two-wave-coupling experimental setup with non-synchronous readout. The results show that the beam fanning noise is little at φ≤30°. The two-wave coupling is investigated in CeKNSBN crystal with orthogonally polarized waves. Compared with the situation of extraordinary polarization, the beam fanning noise is effectively suppressed, and the diffraction efficiency of volume grating is greatly improved.