Abstract: The coupling efficiency of the amplifier and the factors affecting the output power improvement are investigated.The pumping source is a fiber coupled laser diode array with radiation at 976 nm,and the gain medium is a D-shaped doubleclad fiber with the length of(4.4 m,) The signal laser is a non-planar ring oscillator.The coupling efficiency for pump and signal are 80% and 44%,respectively.Output power 6.65 W was obtained when the launched pumping power is 24 W and the signal power is 200 mW.In experiment,the input signal was not saturated,so the amplification has the potential to be improved.