Using the AOM active mode-locked Nd∶YVO₄ laser signal light system and a Yb³⁺-doped D-shape double-clad fiber,a fiber amplifier is setup which has a 320 MHz laser pulse output. The fiber amplifier has a 20 dB signal gain output at 1064 nm,with the average power 1.02 W. It can be used in free-space laser communication system as emission head. The experiment is composed by the high repetition frequency mode-locked laser as signal light,the Yb³⁺-doped fiber for amplifier,and double frequency green light. At the same time,some influence factors of self oscillation spectrum of the fiber amplifier system are investigated. At last,the experimental results are analysed and discussed,and the improving measures for the system put forward.