An automatic method to obtain the size and total number of maize corn was presented. Corn grains are fast fed by vibrating feeder. Maize kernel image was accurately captured by, using error–free match between conveyor belts and linear array camera. Post processing of binary kernel image, removing impurities, filtering and spliting adhesions grain was done to get length, width, and total number of corn grain. The effects of different thresholds and different adhesion grain treatments on the measurement results were studied during image processing. By testing 100 samples of different varieties, the results show that the error of the measurement is the smallest when the threshold number is set to 24 and the average area method is used. Compared with the manual measurement, the correlation coefficient of maize grain total grain number, grain length, grain width is 0.999 3, 0.900 0, 0.930 0, respectively, and the average relative error is 0.26%, 3.85%, 3.63%, respectively.