Abstract: Derived from the Maxwell-Bolth equation, the propagation and amplification equation of the broadband pulses are obtained, and the propagation and amplification of the broadband pulses in Nd glass are numerically simulated by Fourier step method.In the gain saturation regime, the gain narrowing is the main factor, which affects the intensity shape, and spectrum distribution is found.The broadening factor for RMS width of them has the similar rule as well.