The supercontinuum generation in the dispersion-flattened and decreasing fiber was theoretically investigated. The research indicated that the dispersion characteristic of the fiber has influence on pulse evolution and supercontinuum generation. Because the dispersion slope of the fiber at the pump wavelength is equal zero, the pulse keeps symmetry while it propagates in the fiber, and the symmetrical supercontinuum is resulted in. It is more suitable for broad supercontinuum generation when the dispersion curve of the fiber is flatter and the distance between the two zero-dispersion wavelengths of the fiber is farther from each other.