In mine blasting operation, the important index to evaluate the quality of mine blasting is the size of ore fragmentation after blasting. The size of ore lumpiness directly affects the later production operation. Aimed at the problem of ore fragmentation determination during the construction of open-pit mines, a method of ore fragmentation determination based on densely matched point cloud data is proposed. First, the highest point and the lowest point in the ore pile are found to calculate the slope of different ore piles; then according to the calculated slope information of the ore pile, point cloud gray information, neighborhood features, etc., a combination of rough extraction and fine extraction is used to perform the calculation; the extracted boundary lines are used as the data of realize the effective segmentation of different ore point clouds; finally, the segmented single ore point cloud is used to estimate the fragmentation and study the ore distribution law. Experiments show that the proposed method can effectively segment a single ore point cloud, and the segmentation effect is good, and the bulk of the ore in the study area is between 0.5-1.0m.