Using the master oscillation power amplification (MOPA) technology, the dual-stages narrow linewidth fiber amplifier with all-fiber structure is experimentally studied. In the fiber amplifier, the narrow linewidth fiber laser with 20 dB spectral width of 0.078 nm is used as the seeding signal, and the side pumped coupler that is made from the fused tapered fiber, and the (6+1) ×1 multimode fiber combiner are used as the pump power coupling components, and the Yb-doped double cladding fiber with single mode core in the wavelength of 1053 nm, the large mode area Yb-doped double cladding fiber are used as the gain fibers in the two fiber stages, respectively. In the second fiber amplification stage, the back propagation light in the pump input end of the (6+1)×1 multimode fiber combiner is monitored and analyzed, which are including the spectra component and the light power. In order to suppress the spurious lasing of the amplification stimulation emission light, the length of the gain fiber is optimized experimentally. At last, the characters of the stable amplification output laser are the peak wavelength 1053 nm, total gain 27.6 dB, output power 16.09 W, and the nonlinear effects are not observed.