将严格耦合波理论与Kogelnik近似理论比较，研究了Kogelnik理论的近似条件。以两种理论的衍射效率特性曲线的相关或衍射效率计算差别作为判断标准，分析Kogelnik耦合波理论的近似条件。分析结论表明，体全息的Kogelnik理论近似条件与条纹密度、折射率调制度和介质厚度相关，其中反射体全息的近似条件还与条纹面倾角相关。

The rigorous coupled-wave theory and Kogelnik's couple-wave theory are compared for researching Kogelnik's approximation conditions. The approximation conditions are analyzed with the judgment standards of the correlation of diffraction efficiency curves or the difference of diffraction efficiencies between two theories. The conclusions in this paper are that approximation conditions of Kogelnik's theory correlate with fringe cycle, refractive index modulation and the thick of medium. The approximation conditions for reflective volume hologram correlate with fringe cycle, refractive index modulation,the thickness of medium and the angle of fringe plane.