An acousto-optic Q-switched fiber laser experimental system has been established, and the multi-peak phenomenon of the output Q-switched pulse has been analyzed. In order to find the Q-switched pulse with less multi-peak number and better shape, we adjust the controllable parameters like the pump power of system, the repetition rate of acousto-optic Q-switch, opening time and rise time. At last, when the pump power is 8 W, repetition frequency of Q-switch is 10 kHz, opening time is 260 ns, and rise time is 150 ns, we have got a Q-switched output pulse with a slightly protuberance in the front, the conversion rate of laser is about 23.6% at the moment. The multi-peak number of output pulse is reduced successfully in the experiment, and the output waveform of Q-switched pulse is optimized. The analysis of the experiment result provides methods for outputting smooth pulse of acousto-optic Q-switched fiber laser.