A narrow bandwidth double clad fiber (DCF) laser is reported.The numerical analysis includes dependence of output power on output mirror reflectivity,fiber length and pump power.In our experiment,a fiber Bragg grating (FBG) was used as the input mirror of the cavity.The Yb 3+ doped DCF was pumped by a laser diode emitting at 975.8 nm.The narrow bandwidth of 0.16 nm single mode laser was obtained.It produced an output power of 421 mW at 1 086.9 nm with absorbed pump power of 684 mW.The slope efficiency was 78.2 %.