Simple and efficient F-P Yb-doped fiber laser with fiber tunable reflectivity loop mirror and fiber Bragg grating as cavity mirrors is brought forward. A polarization controller is twined in the loop mirror and the optimum output ratio can be obtained easily, and the trouble of selection of different reflectivity output mirror is avoided. Also fiber loop mirror has wideband reflective spectrum, which can improve the pump efficiency and give more output power. The output power of 5.65 mW, slope efficiency of 19% are obtained when pump power is 51 mW and fiber length is 7 m.