Multi-wavelength switchable optic fiber laser can select one or several wavelengths of the multi-wavelength. It supports the dynamic allocation of the wavelengths in the optic network, which adapts the development of the wavelength division multiplexing(WDM) and dense wavelength division multiplexing(DWDM) systems with more channel numbers in modern optical fiber communication system. A self-seeded multi-wavelength switchable Erbium-doped fiber laser is proposed and experimentally demonstrated in this paper. The Erbium-doped fiber is pumped by a 980 nm pump to produce 1 550 nm spectra, and it returns back through a ring structure so as to realize the self-excitation and to reduce the cost of the experiment. A Sagnac ring with two segments of polarization maintaining optical fibre is used as a filter. By adjusting the rotation angles of the polarization controller in the circle of Sagnac filter, the cavity gain of the Sagnac filter changes. It allows the wavelengths reflected by the fiber Bragg Grating pass selectively, so as to realize the wavelength switchable function. The experiment proved that it is an effective way to realize the multi-wavelength switchable function through adjusting the cavity gain of the Sagnac Filter and letting the wavelengths pass selectively.