In order to compensate for the gain narrowing and gain saturation effects, and also to improve the signal to noise ratio of the output high-power laser pulse, lots of attention have been paid to the spatial distribution, the temporal profile, as well as the spectrum reshaping in the design of kilo-joule peta-watt chirped pulse amplification (CPA) systems. In this paper, a new method for the spectrum reshaping is proposed, which utilizes a multilayer dielectric thin film reflector with specific construction to realize the spectrum reshaping of the chirped pulse laser in large energy and high power Nd:glass CPA system. The results show that the reflectivity distribution of the multilayer dielectric film reflector can be controlled effectively only if the parameters of the thin film reflector are chosen appropriately. The spectrum modulation radio can be varied over 60% under the condition that the phase of the reflecting light remains nearly constant. The thin film reflector designed for spectrum reshaping of the Nd:glass CPA system with the central wavelength of 1053nm exhibits a bandwidth of reflect light of 196nm, the chromatic resolving capability of about 0.1nm and the phase aberration in the range of the tens of nanometer of up to 12mrad, which can meet the requirement of the “Senguang-Ⅱ” kilo-joule peta-watt reconstruction project.