In the petawatt (PW)-class ultra-intense ultra-short laser system based on the Ti∶sapphire (Ti∶S) chirped pulse amplification (CPA) technique, there is gain narrowing and redshift of the spectrum caused by the different spectral emission cross section and the effect of saturation amplification. The redshift of the spectrum appears widely in the process of laser amplification, especially in the high energy and saturation amplification process. In this paper, aiming at the spectrum control of Apollon-10 PW, we theoretically propose a new spectral shaping technique to suppress redshift of the spectrum in saturated laser amplifiers based on optical-optical synchronization amplification. The technique is based on the experimental results of 5.0 PW laser system in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. The technique is based on the conventional amplification model and optical-optical synchronization amplification through introducing the pump with short pulse width in power amplifier. The technique does not need to introduce other optical devices and does not introduce additional losses, and its operation is simple. Theoretical simulations show that the technique can effectively realize the shaping of amplified spectrum, which suppresses the redshift effect of the spectrum.