Leaf is a vital organ of the plants to survive and it is one of the important parts in building a plant growth model. Detecting green crop leaf area plays an important role in the establishment of the plant growth model and the assessment of the plant growth state. A kind of efficient detection algorithm of green crop leaf area is put forward and the content mainly includes three parts. Firstly,it intro-duces the process of green crop pictures which involves green extraction,binarization processing and filtering denoising. Secondly,it dis-cusses the calculation process of green crop leaf area including camera calibration,unit pixel area calculation and target pixels statistics. At last,the result of algorithm is verified. The experiment shows that the error of the leaf area detection ranges from 0. 20% to 1. 29% and the average error is 0. 84%. It can be seen that the algorithm proposed in this paper has a high feasibility.