In order to study the propagation characteristics of super-Gaussian pulse in super-Gaussian dispersion decreasing fiber with different steepness, the nonlinear evolution of Gaussian pulse in the super-Gaussian dispersion-decreasing fiber was numerically simulated by using the nonlinear Schrdinger equation and the stepwise Fourier transform method. The theoretical analysis and experimental verification of the super-Gaussian pulse in the time domain and frequency domain were carried out with consideration of dispersion and nonlinear effect in the abnormal dispersion zone. The results show that, when the steepness m=4, the super-Gaussian dispersion-decreasing fiber has the best transmission characteristics, so it is concluded that the higher the steepness m is, the better the transmission characteristics of pulse will be.