In order to obtain pulse width of hundred femtoseconds in optical parametric chirped pulse amplification system, the spectrum of the seed pulse is shaped to compensate gain narrowing, gain saturation and self phase modulation. A new arbitrary spectral shaping method for chirped seed pulse can be achieved with pump pulse time shaping in optical parametric amplification. Compared with the spectral shaping method for chirped seed pulse before optical parametric amplification, the new method will not bring the spectral phase modulation, and the procedure of spectral shaping and energy amplifying will go on in the same time. The results from numerical simulation indicate that the two methods require the same stability for input pump and seed pulse. To insure the amplified signal energy stability is better than ±5% after parametric coupling, the peak intensity change of pump pulse must be controlled less than ±1%, and the peak intensity stability of seed pulse can be controlled in the range of ±3%.