In order to identify the number of maize plants without damage, the four station scanning method was used to collect the data of corn field point cloud from different perspectives by using FARO focus s70 laser scanner. A registration algorithm based on automatic extraction of target ball was designed. The point cloud data obtained by each station was accurately registered, and the complete corn field point cloud data was obtained. The registration accuracy was analyzed by the fitting error and standard deviation of the target ball. For the three-dimensional point cloud data, the stem point cloud was separated from the whole corn field point cloud by using the sampling consistency algorithm based on the cylinder characteristics, and the number of corn planting plants was counted. The results show that the standard deviation of the standard fitting of the target ball is between 0.1mm and 0.7mm, which meets the requirements of the instrument measurement accuracy. The fitting error is between 2mm~5mm, which can meet the requirements of 5mm in large scene measurement registration error. The recognition rate of maize plant number was 86.1%~92.1%. This result is helpful to the practical application of maize plant number identification in farmland environment, providing data base for crop yield estimation and theoretical method for intelligent agricultural research.