Numerical simulations based on generalized nonlinear Schrdinger equation were used to study the suppression of residual pump component of supercontinuum generated in dispersion-flattened dispersion-decreasing fibers.The results show that the shape of a supercontinuum spectrum is uniquely specified by the input soliton order N,the normalized quadratic dispersion coefficient Δ2 and the normalized effective fiber length ξ0.For a pump pulse with a given N and a given value of Δ2,the shape of a supercontinuum spectrum depends on ξ0.By appropriately choosing ξ0,the residual pump component can be suppressed effectively and a supercontinuum with desirable spectral flatness can be obtained.In order to obtain the optimal value of ξ0,S-factor is introduced to estimate the fluctuation of supercontinuum spectrum.The smaller the value of S-factor,the flatter the generated spectrum.Keeping N and Δ2 constant,S-factor of the generated supercontinuum spectrum for different value of ξ0 was calculated.When S-factor reaches a minimum value,the residual pump component is suppressed to the utmost extent and a flattest supercontinuum spectrum is obtained.The corresponding ξ0 is the optimal value of ξ0.The optimal value of ξ0 for the pump pulses with soliton order N in the range 1.0≤N≤2.2 was calculated.It is found that when N decreases,the optimal value of ξ0 increases.To generate a supercontinuum spectrum with weak residual pump component,lower-order soliton pulses are preferable to higher-order soliton pulses.