We use fundamental matrix (F-matrix) method derived from coupled wave theory to simplify the diffraction simulation of chirped volume Bragg grating (CVBG) and it can be applied to arbitrary grating phase profiles. With the F-matrix method, we study the diffraction in CVBG. The spectral response of CVBG is a gate-like function, and the passband width of spectral response is related to the product of grating thickness and spatial chirp rate. The peak diffraction efficiency of CVBG increases monotonously as the amplitude of refractive index modulation increases. Incident beams with different wavelengths will be mainly diffracted at different depths of CVBG to match the Bragg condition.