Abstract: Crops acreage estimating is the fundamental work for government's agricultural information monitoring on a national scale. Measuring with onboard estimation system is one of the approaches to perform ground truthing. In this article the authors propose a system, namely Categorized Crops Acreage Onboard Estimation System(CAOES) Based on Image Identification System, CAOES for short, and analyze its principle and configuration. Then the authors give the vision measuring model for acreage estimating and its precision evaluating. The test results indicate: 1)FA lens with 8mm fixed focus reach a balance between the two demands of vertical visual field and image detail;. 2) with the software, the aperture and exposure index can be self-adapting to the natural light to meet the demands of image analysis ; 3) the experiential model has bigger correlation coefficient and more steady predicted value than quadratic polynomial model; 4) this system may be more laborsaving, impersonal and in time.