The ultrasonic borehole imaging system while drilling is a cutting-edge technology and equipment in the field of measurement and control while drilling. It has the advantages of accurately reflecting wellbore shape, identifying cracks, pores and bedding characteristics, and can be used for real-time monitoring and evaluation of wellbore engineering conditions and quality. It can effectively reduce drilling risks and costs, improve drilling efficiency and reservoir drilling rate. The four-channel ultrasonic signal acquisition system is the core functional unit of the downhole instrument of the ultrasonic borehole imaging system while drilling. Its performance affects the subsequent signal processing and the realization of various algorithms, and determines the resolution and accuracy of the ultrasonic borehole image. In order to meet the reliability and stability requirements of multi-channel ultrasonic travel time and echo amplitude information acquisition in the ultrasonic borehole imaging system while drilling, a four-channel ultrasonic signal acquisition system with FPGA + ADC + SDRAM as the core architecture is developed. The system takes FPGA as the core control chip, and realizes the real-time acquisition, caching and communication of four-channel ultrasonic signals through the logic control of four-channel synchronous ADC and SDRAM. Based on the indoor experimental platform, the four-channel ultrasonic signal acquisition system designed and developed is tested and verified. The results show that the system can realize the functions of four-channel ultrasonic analog signal preprocessing, analog-to-digital conversion, data acquisition, data caching and data communication. Applied to the indoor experiment of ultrasonic imaging, the ultrasonic imaging under two-dimensional plane scanning is realized, which lays a solid technical foundation for the independent research and development of ultrasonic borehole imaging system while drilling.