A switchable multi-wavelength erbium-doped fiber laser based on double Sagnac loop filter was proposed. The parallel double Sagnac loop filter was consisted of polarization-maintaining fiber and few-mode fiber. Its structure was simple. And the multi-wavelength output of erbium-doped fiber laser was realized by the comb filter property. Adoptting transmission matrix method, the characteristics of double Sagnac loop were analyzed in detail. When using the double Sagnac comb filter in linear cavity laser system, a switchable multi-wavelength fiber laser with stable single-, dual-, and triple-wavelength outputs can be obtained at room temperature by adjusting the polarization controllers and changing the polarization state in the cavity. At the same time the lasing wavelength locations also can be switched. The results show that the side mode suppression ratio (SMSR) of the output wavelength is more than 34 dB. In the test of the stability, the maximum wavelength shift of output wavelength is less than 0.05 nm, which has stable output and can be applied in fields such as wavelength division multiplexing and all-optical communication systems.