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A GPRS/GSM hybrid communication method is designed to develop a low-power RTU (remote terminal unit) for sensor signal acquisition and data transmission of distributed monitoring systems in industrial fields. The hardware architecture, key technology and transmission protocol of RTU are illustrated. Considering to GPRS network congestions, the reliability design of RTU is analyzed. When GPRS connection fails, the RTU switches to the SMS mode to resume the data transmission such that data integrity is ensured. Besides, the RTU is provided with multiple data sampling interfaces and low power mode. The data transmission experimental results show that the average GPRS transmission delay is 1.126~2.669 s, and the data loss rate decreases to 0 in hybrid communication from 6.94%, in single GPRS mode.