Supercontinuum generation from optical fibers with different group velocity dispersion (GVD) was simulated and calculated in details. It is found that flat and wideband supercontinuum cannot be obtained in anomalous and zero GVD regions because of fiber higher order nonlinearity (intrapulse Raman scattering) and higher order dispersion (TOD). Nevertheless, the broader and smoother supercontinuum spectrum can be obtained in normal GVD region. It is also found that a dispersion flattened fiber with small normal GVD is most suitable for flat and wideband supercontinuum generation. A super wide supercontinuum more than 300 nm with the spectral intensity fluctuation less than 10 dB was generated from such a fiber through increasing the pump power of the pulse.