Abstract: To solve the shortcomings of indirect LAI measurement methods which seldom considered the factors of single isolated canopy, leaves overlapping each other and the image processing speed slowly, the intermittent model avoiding leaves overlapping was established based on the main influential factor of single isolated citrus fruiter LAI'S measuring system (α＜0.05) by orthogonal experiment . Then automatic acquisition possible was realized by adopting three dimensional walking mechanisms, and an automatic measuring system of citrus LAI was developed based on infrared transmission using the LabVIEW platform. The hardware system was composed of control module, running gear, signal conditioning model, data acquisition card and PC, of which the demarcated average absolute relative error was 11.11%. With the running gear scan, locate and collect automatically in S shape, 45 citrus trees in the citrus garden of the College of Engineering of South China Agricultural University were tested. With the LAI value computed from direct method and sampling method as true values, the average absolute relative error was 31.4%. Compared with true values, average absolute relative error of the measured value from plant canopy analysis's professional version was 29.8%. Since the errors of the two systems were similar, the system proposed could meet the requirement of LAI test.