Using cascaded stimulated Brillouin scattering (SBS), the self-exciting Brillouin erbium-doped fiber laser (BEDFL) is a multi-wavelength source at room temperature. The multi-wavelength output of the BEDFL with a high-birefringence Sagnac loop filter is tunable by adjusting the polarization controller (PC) in the Sagnac loop. At the same time, dual Brillouin bands appear during the experiment. The influences of the bandwidth of the Sagnac loop and the pump power at the 980 nm on the multi-wavelength output are investigated in detail. A multi-wavelength band with 52 lines is achieved when the bandwidth of the Sagnac loop filter is 83.3 nm and the pump power at the 980 nm is 260 mW.