To improve detection efficiency of tobacco strip size distribution in the process of tobacco leaf threshing and redrying, a quick on-line measuring method of tobacco leaf area for analyzing tobacco strip size distribution was investigated. Leafs area were measured on-line by analyzing the leaf images on the conveyor. The field curvature blur of line camera was restored by means of space variant blur matrix, and the image distortion was rectified by Zhang Zhengyou calibration method. A threshold segmenting method which uses the difference of R and G component was proposed. The segmentation method which is insensitive to noise and illumination can segment the leaf image form background accurately. An efficient method of leaf area accumulating was proposed to replace the image stitching and the problem of single leaf partitioned in two images was solved. The parallel image processing software was written by using multi-threading technology. The repeatability tests results show that the image processing speed reaches to 22 frame in each second, the relative error is less than 0.50% and the coefficient of variation is less than 1.01% which is in the 100~2500 mm2 measuring range. 