In the ultrashort pulse high-energy laser system based on chirped pulse amplification technique, multilayer dielectric grating with good output waveform and high laser induced damage threshold plays an important role. Based on Fourier spectral transform and rigorous modal method, optical characteristic of multilayer dielectric grating under irradiation of ultrashort optical pulse is analyzed. The results show that the reflected pulse at the -1 order exhibits asymmetrical Gaussian shape with oscillatory tail in the front edge and decreasing energy when the reflection bandwidth is narrower than the frequency bandwidth of the incident pulse with Guassian shape. The effect of structure parameters of multilayer dielectric grating on the reflection bandwidth are discussed in detail, which provides guidance to the design of multilayer dielectric grating with desired reflection bandwidth. Finally, near-field distribution of multilayer dielectric grating is analyzed to study its damages induced by ultrashort pulses.