In order to achieve stable multi-wavelength output, a multi-wavelength fiber laser based on nonlinear polarization rotation(NPR) of semiconductor optical amplifiers(SOA) is proposed and demonstrated. Due to the NPR effect of SOA, the intensity-dependent loss (IDL) is induced by the combination consisting of SOA and other polarization devices to suppress mode competition within homogenous broadening linewidth of SOA. Stable multi-wavelength lasing with wavelength spacing as small as 0.63 nm and wavelength number up to 35 is achieved at room temperature. Moreover, 12 nm wavelength tuning is implemented by tuning polarization. Finally, experimental investigation is carried out to show the stable multi-wavelength output with smaller wavelength spacing can be achieved by increasing the length polarization-maintaining fiber (PMF).