The spectrum of seed pulse is necessary to be shaped to compensate the gain narrowing effect of spectrum in the chirped pulse amplification (CPA).A scanning amplitude limiting approach for spectral shaping of chirped laser pulse is proposed based on the Mach-Zehnder interferom eter (MZI) built in a KTN electro-optic crystal.The effect of the steady-state voltage and the dynamic voltage appli ed to the KTN electro-optical crystal on the transmission spectra function is researched.And the influence of the tim e-delay of the voltage variation relative to that of frequency and the own voltage deviation on the spectral shap ing is discussed.The simulations shows that the voltage applied to the electro-optical crystal can be invers ely calculated according to the needed spectrum shape,and the transmissivity of each frequency component of chirped pu lse is controlled with time, which leads to the spectral shaping of chirped pulse.The approximately flat-to p spectral shape is obtained which is almost the same as the needed spectrum shape by the proposed scanning amplitude limiting shaping approach,for the first-order Gaussian pulse with central wavelength of 800nm,chirp paramete r of 21230corresponding to 20nm bandwidth.Furthermore,with the increases of the time-delay and voltage deviatio n,the shaped spectral shape is farer away from the needed spectrum shape.In order to obtain the identical pulse spec trum as needed,it is necessary to make sure that the voltage matches with the frequency in time and the unf avorable deviations are reduced.