Abstract: As the monitoring system for grain depot has the characteristics of multiple measuring points, far transmit distance, poor expansion and hardly mobility, a new method using three layer reader networks for wireless monitoring the temperature and humidity of grain depot was proposed. A sensor-tag integrated with the sensor SHT75, the microcontroller MSP430F149 and the RF communication module NRF905 was designed. The temperature and humidity signals of the grain depot were acquired by sensor-tag, packaged with the current time and the address code information by front-side reader, and transmitted wirelessly to the terminal reader and control center by relay readers. The experimental results show that the system has the characteristics of good expansibility, long transmit distance(≥128?m), simple routing and easy positioning.