The optical parametric chirped pulse amplification (OPCPA) is a reversible nonlinear course. When the signal reaches its peak density, the pump power has been almost depleted. After this point,the over-saturating OPCPA course begins and the energy from the signal and idler reverses to the pump. A new method of the chirped-pulse spectrum shaping is put forward in this paper based on the above course. The theory of the new spectrum shaping method is explained by simulation. Also by simulation it is shown that by varying the pump intensity or adjusting the phase matching angle or changing the pump waveform, the output of spectrum shaping can be effectively controlled; even when signal and pump pulses are under the proper synchronous conditions, a frequency shift occurs at amplified signal, and the spectrum red-shift induced by Ti:sapphire saturation amplification may be suppressed.