Abstract: Geometric features measurement of maize ear is the key technology of maize cultivar automatic analysis. But it is difficult to measure the geometric features(total length, width, bald, volume, etc) of maize quickly and accurately for the complexity of the background image. In this paper , three regional image enhancement model was constructed according to the distribution characteristics of maize gray image. Then the morphological image processing methods were applied to segment the enhanced image and calculate the background plate scale. Based on the above background plate scale, the geometric feature parameters of maize could be computed accurately. In addition , an analysis was made in comparison with manual measure of maize feature. The comparison result showed that the image processing algorithm based on the background plate scale could measure the maize geometric feature accurately. The accuracy rate was above 96.01%. This algorithm raised in this paper can replace the traditional maize cultivar measure and realize the maize cultivar automatic analysis, which will play an important role in maize variety extension and breeding.