Field information collection is the key technology of precision agriculture. To obtain the yield information, an impact-type grain flow sensor is developed for the yield monitor system. The grain flow sensor consists of a mechanical unit and an electrical unit. The mechanical unit is composed of an impact plate, a sensitive bar, some strain gauges, etc. The strain gauges are stuck on the sensitive bar. When grain flow impacts the plate, the bar bends and the bridge circuit consisted of the strain gauges outputs electrical signal. The output of the sensor is voltage signal. On the basis of the static experiments and indoor experiments, field experiments are finished in Baoding of Hebei Province and Jiamusi of Heilongjiang Province. Harvesting crops are wheat and rice. The results show that the sensor has higher linear property and the accuracy meets the requirements of the precision agriculture.