The invention discloses a crop effective grain number measuring method. According to the crop effective grain number measuring method, the grain distribution images and accurate grain weighing data of crops in different varieties are obtained through photographing and weighing respectively; the number of the grains of the crops is extracted preliminarily through independently-developed data processing software and based on a mathematical morphology principle and a digital image processing technology; and the number of the grains is corrected by using the weighing data of the grains, so that imperfect grains are eliminated, and therefore, the extraction accuracy of the number of effective grains can be improved. With the method of the invention adopted, image preprocessing, and grain number accurate and quick identification and batch extraction can be carried out on photos with different grain conditions, and crop grain extraction accuracy can be ensured, and extraction speed can be greatly improved.