A high precision surface acoustic wave measuring instrument based on FPGA equal precision frequency measurement and automatic gain control(AGC) circuits is designed. The measuring instrument collects the sound wave through the surface acoustic wave sensor and converts it into an electric signal and limits and shapes the signal through the AGC circuit and the Schmitt trigger to convert it into a square wave of the measurable frequency. Finally, the frequency measurement circuit is realized by the FPGA frequency measuring circuit, and the result is transmitted to the single chip microcomputer for display. The test results show that the instrument can measure the signal frequency in the frequency range of 100 Hz~100 kHz. The maximum measurement error of the system is 12%, the frequency range is wide, the precision is high, and the stability is good.