Abstract: By combining a large mode area(LMA) Yb-doped double cladding fiber(YDCF) amplifier with a solid state seed laser, an fiber amplifier, whose single pulse power was about 1 mJ and narrow linewidth was about 0.1 mJ, was reported. Different from the traditional one-stage fiber amplifer with solid state laser seed source, a two-stage large diameter fiber amplifer was used in the YDCF amplification system. The two-stage fiber amplifer was much simpler in the aspect of coupling the spatial seed light into the fiber. A variety of methods were used to suppress nonlinear effects during the amplification process. Obvious nonlinear effects such as SBS, SRS, were not observed in the output, with the SNR exceeding 30 dB. After YDCF amplification system, the output average power was amplified to 10.07 W. Compared to the power of seed, which was about 0.38 W, the output was increased by 14.23 dB. At the pulse repetition rate of 10 kHz, the pulse energy is about 1 mJ, with the pulse width of 50 ns. The beam quality M2 of the output laser is 3.72. The pulsed fiber amplifier with narrow linewidth and high pulse energy will be very useful in many practical applications, such as laser remote sensing, laser measurement and nonlinear frequency conversion and so on.