Abstract: Yb-doped double-clad fiber amplifiers of different lengths were pumped by a fiber-coupled diode laser emitting at 976nm.A non-planar ring oscillator was used as the signal source emitting CW single frequency radiation at 1064nm.When the pumping power was 49.6W and the signal power was 200mW,up to 16.1W single-frequency laser was obtained in a 10m-long fiber.The relation between fiber length and output power was analyzed by changing different lengths of fiber as the gain media.The emission spectrum was discussed.Single frequency operation was verified by a Fabry-Perot interferometer.