In order to achieve stable narrow linewidth and high-power laser output, an Er3+/Yb3+ co-doped narrow linewidth fiber laser based on cascade amplification is designed, its linewidth and stability are discussed in detail. The two-stage structure is adopted for amplifier to decrease the spontaneous emission noise of final output, and the single clad Er3+ doped fiber is adopted for pre-amplifier as gain medium. The double clad Er3+/Yb3+ co-doped is adopted for the master amplifier. Experimental results show that the changes of stabilities for laser outputs cannot be monitored obvious clearly, while the laser is amplified by various amplifiers. However, due to the relaxation oscillation and the self-phase modulation which result by the intensity fluctuation of self-pulsation, the different levels of linewidth broadening are observed.