Abstract: The broadband nanosecond shaped laser pulse obtained by chirped pulse stacking(CPS) method can make the output stacked pulse meet the requirement of the inertial confinement fusion(ICF). However, temporal pulse shape modulation will come forth due to the pulse coherence of stacked chirped pulses, so will spectrum modulation. Factors influencing stacked chirped pulse waveshape and characteristics of the amplification process of stacked chirped pulse were studied. Results show that the evolution law of stacked chirped pulses is consistent with that of narrow band pulses, and the time modulation structure does not change in the amplification process. However, the spectrum modulation changes, which could be preliminarily inferred from the nonlinear effect. The stacked chirped pulse has a gain