A set of grain moisture detection device based on incident microwave was designed, and the STC89C52 chip was used as the main processor to control the execution order of each component. Moreover, the photoelectric switch was used to keep the amount of the loading material in line. In order to eliminate the influence of temperature, it was detected in real time, and the temperature compensation model is established. To avoid the thermal effect of microwave, the sequential control system was applied to collect temperature and microwave signals, ensuring the accurate measurement of grain moisture. The results showed that the correlation coefficient between actual moisture content and microwave moisture content was greater than 0.96, and it could meet the requirements of actual test.