A switchable mode-locking fiber laser is proposed by means of fiber Bragg grating (FBG). The FBG plays two key roles, the switchable wavelength operation and the spectral filtering effect, on the proposed laser. The switchable single-wavelength mode-locking operation, lasing at either 1545.25 or 1548.34 nm, corresponding to the central wavelengths of the FBGs, is obtained by appropriately rotating the polarization controllers (PC). In addition, the dual-wavelength mode-locking operation is observed with proper PC state. The switchable mode-locking operation attributes to the wavelength-dependent loss mechanism and the spectral filter formed by PCs and FBGs.