A system based on phase difference method for measuring the sound velocity of seawater is designed.Taking advantage of the linear relationship between phase and time as well as the phase difference change of signal to achieve high precise measurement of sound velocity of seawater. The system adopts the combination mode of dual port RAM（ DPRAM） memory cell and external memory interface（ EMIF） to realize high-speed and real-time data communication between field programmable gate array（ FPGA） and microcontroller unit（ MCU）. On the basis of FPGA and C8051 MCU hardware

through high-speed AD chip sampling

achieve data storage and processing.The phase difference measurement implements the uncertainty of 0. 01 comparing with standards

and the precision of seawater sound speed measurement is prior to 0. 02 m/s（ k = 1）. The experimental results verify the reliability of the proposed scheme.