From the nonlinear Schr?dinger 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 high nonlinearity of the photonic crystal fiber are investigated. The forming mechanism of supercontinuum generation by using quasi-continuous-wave as the incident source was also studied. It is shown that the higher pump power and wider pulse width generate wider supercontinuum. In addition, the widening at the longer wavelengths of the supercontinuum is limited 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.