A method for flatly ultra-broadened supercontinuum generated in anomalous dispersion region of a dispersion-shifted fiber is introduced. Supercontinuum generated in anomalous dispersion region of dispersion-shifted fibers due to compression effects of higher-order soliton is studied in detail through numerical simulations. The results show that the dispersion slope of dispersion-shifted fiber is crucial to supercontinuum generation. It also shows that both the peak power and pulse width of pump pulse affect the spectral width and flatness of supercontinuum markedly, but higher-order nonlinear effects can be ignored. A flatly ultra-broadened supercontinuum near 300 nm with the spectral-intensity fluctuation less than ±2 dB is obtained by optimizing the relative parameters.