The Bragg deviations proterties of volume holographic optical elements (HOEs) and compensation are Studied. And the allowable deviations of wavelength and angle from Bragg condition are discussed. Finally, tho authors como to a conclusion that at some modulations the higher diffraction efficiencies of VHOES can still be obtained off Bragg condition and the value of allowable Bragg deviation is larger in higher modulation. The experimental resulta are given in this paper.