Some wrong points are found about the formula of the refractive index distribution in volume hologram grating recorded linearly in some literatures when the nonlinear recording spectral properties of volume hologram are discussed. The formula of the refractive index distribution is discussed again when recorded linearly. The light intensity ratio and the total light intensity refractive index modulation coefficient are added into the formula, and the diffraction spectral of gratings versus different light intensity ratio and total light intensity refractive index modulation coefficient are calculated in the coupled-wave theory. The calculational results show that the primary peak values of diffraction spectrum reduce slightly when the light intensity refractive index modulation coefficient or the light intensity ratio decreases, but the secondary peak value, decreases obviously and the bandwidth becomes narrow greatly with those conditions.