The high-speed fiber acousto-optic modulator based on InP was introduced in this paper．The design principle of high-speed fiber acousto-optic modulator was analyzed．The design parameters of high-speed fiber acousto-optic modulator are obtained by simulation. A 300 MHz fiber acousto-optic modulator with optical wavelength of 1 550 nm was fabricated. The results showed that the insertion loss is 2.8 dB, extinction ratio is 49 dB and rise time of optical pulse is 6.34 ns.