In order to realize the switchable multiwavelength oscillation, a fiber ring laser based on a multimode interference filter and a birefringent filter was proposed and demonstrated. The filtering characteristic of the cascaded fiber filters was analyzed theoretically, and the irregular side modes of the multimode interference filter can be effectively restrained by cascading birefringent filter. The Polarization Maintaining Erbium Doped Fiber (PMEDF) is utilized to serve as gain medium and a part of birefringent filter simultaneously, the length of the multimode fiber and PMEDF are optimized to match the same wavelength spacing, the filtering period of the cascaded fiber filter is 4.89 nm. The laser could switch to output single, dual, triple and quadruplewavelength by finely adjusting polarization controller in the experiment, sidemode suppression ratios of lasing wavelengths are more than 40dB, and wavelength fluctuations are less than 0.1 nm during a period of 1h.