The saturable absorber Bismuth Telluride nanosheets are synthesized via optical self-assembly method, and the nonlinear optical response characteristics are obtained. By introducing the saturable absorber into the Er-doped fiber laser, the Q-switched fiber laser can deliver the pulse laser with pulse duration of 2.91 μs , wavelength of 1564.94 nm with the pump power of 170 mW. With the modulation of continuous wave laser on nonlinear absorption devices, the pulse duration and repetition frequency tunable Q-switched fiber laser is realized.