Grain yield map is the important means for analyzing and managing data of yield monitor system. The authors developed a yield mapping system software for the requirement of national grain yield monitoring system. The main function and system layer frame of the yield map software are confirmed by analyzing the crop yield distribution map system in existence. Inverse distance to power algorithm is selected as yield data interpolation method. The method of data filtering and 3σ theorem were used to filter the big errors on yield data. The yield mapping softwares with spatial data interpolation, error data filtering, yield data statistic distributing, raw yield map, grid yield map and contour yield map functions were developed.