High voltage microprocessor relay protection devices need to sample and manage multi-channel AC electrical data. Sampling synchronization and real-time performance of data processing are key factors which affect protect performance. A multi-channel synchronous sampling technique based on high-speed serial communication is proposed to improve synchronous sampling and data interface mode. The technique can further ensure sampling synchronization based on existing hardware. It can also enhance the real-time and parallel processing performance of sampling data transmission and storage. This technique has good scalability and high reliability. It meets the requirements of different types of high voltage microprocessor relay protection devices， and is especially suitable for situations which require many channels of analog sampling loop. This technique has been tested in a series of high voltage relay protection devices and has been used in engineering practices.