Based on the coupled wave equations that describe the interaction of laser pulse with volume gratings, the diffraction properties of volume gratings illuminated by linear chirped pulse with various input pulse widths and chirped parameters are studied. The properties of the spectral intensity and phase of diffraction pulses are investigated. The calculations demonstrate that the diffraction spectral width is influenced by the input pulse width, chirped parameter and the spectral width of the volume grating. With the incident pulse width increasing, the diffraction spectral width is reduced, but the diffraction efficiency increases. With the increase of the chirped parameter, the diffraction spectral width is increased, but the diffraction efficiency decreases. The change of diffraction phase spectra is increased with the increase of the input pulse width and the decrease of the chirped parameter, and the curve of the phase spectral distribution is asymmetric. We also find that the Bragg diffraction of the volume grating can shape the linear chirped pulse laser, and keep perfectly the linear chirp characteristic of the diffraction pulse, when the grating vector and input angle are selected properly.