The utility model provides a mode locking fiber laser belongs to the fiber laser field, mode locking fiber laser includes pumping source and mode locking laser resonator, and mode locking laser resonator includes the inclined to one side wave filter of reflection part, gain fibre, guarantor of coupling in proper order and is used for the saturable of mode locking to absorb the mirror. The pumping light that the pumping source sent gets into the gain fibre and generates the pilot light, the pilot light gets into saturable absorption mirror through protecting after inclined to one side wave filter is handled to the pilot light of presetting the?polarization?direction and presetting wavelength coverage, returns after the saturable absorbs the mirror mode locking and protects inclined to one side wave filter, returns the pilot light to?re -enter?the gain fibre of protecting inclined to one side wave filter, imports to the reflection part behind the optical fibre?amplifier that gains, satisfies the part output of reflection part transmission condition in the pilot light behind gain optical fibre?amplifier. Compare in traditional mode locking fiber laser, the utility model provides a mode locking fiber laser simple structure, it is reliable and stable, the engineering application of being convenient for.