In this paper, the design idea and application experiment of fiber optical acoustooptic modulator for pulse picking up and frequency reduction in the ultrafast fiber laser systems are introduced. The working principle of acoustooptic modulators is described. The function of synchronization, frequency demultiplication and analog modulation under 46.6 MHz multi femtosecond laser pulse have been realized, which can meet the user requirements. A kind of acoustooptic pulse picker with the optical pulse rise time of 10 ns and insertion loss of less than 3 dB has been developed.