Ag Leader grainyield monitor system was introduced. The yield monitor system experiment was carried out on the domestic medium and small combine harvester. The grain yield system was mainly composed of multi-channel sensors including grain flow sensor, terminal display processor and GPS system. First, the calibration experiment of system was executed. And then, the harvesting experiment of winter wheat in the field was performed and the acquired data were processed. With the analysis of spatial autocorrelation method, yield data presented high dependence within 20m. Semi-variance analysis showed that the variation of the yield data was obvious which presented the property of aggregated distribution. The yield map based on Kriging interpolation showed the trend of patch distribution and the properties of aggregated distribution. The experimental results could provide necessary theoretical evidence for the application of precision agriculture.