An all-fiber based polarization output mode-locked laser is proposed. Without a band-pass filter in the oscillator, stable mode-locked pulse train in the all-normal dispersion region is obtained when the polarization output of fiber polarization splitter and the birefringence filtering effect of fiber are used. The repetition rate of pulse is 2.2 MHz and the single pulse energy is 100 nJ. The single-wavelength and dual-wavelength mode-locked output are experimentally obtained when we adjust the intra-cavity polarization by an in-line polarization controller, and the stable dark soliton pulse is observed at 1 μm. The evolution of the intra-cavity polarization is the key to obtain different mode-locked states. Under the dual-wavelength mode-locked state, the wavelength tunable width can reach 12 nm. The system transmission function is used to theoretically analysis the principle of wavelength tuning based on intra-cavity polarization controlling.