Abstract: From the basic equation that governs propagation of picosecond optical pulses in fibers, by using simulation method, quasi-continuous-wave supercontinuum generation by using the modulation instability of single mode fibers and the highly nonlinear of the photonic crystal fiber are investigated. The forming mechanism of supercontinuum generation by using quasi-continuous-wave as the incidence source has also been studied. It is shown that, the higher of the pump power, and the wider of the pulse width, the more wide of the supercontinuum. In addition, the widening at the longer wavelengths of the supercontinuum will be limit by the length of the supercontinuum, that is to say, in order to obtain a smoother and broader supercontinuum, one must use an optimal fiber length.