Adopting virtual instrument software development platform——LabView and image processing software package——IMAQ Vision to develop interactive measurement application system, and a dairy cow conformation linear appraisal system was built based on image processing. The blue color background was selected by the system, the image contrast and the localization accuracy were strengthened, and the image processing difficulty was reduced. The S value from the HSL model was extracted to realize image grizzled processing, and the image noise through the medium filtering was reduced. The research showed that with the template match method to distinguish the characteristic point, the determination rate of accuracy reached above 90%. Compared the results appraised by computer with those by appraiser, the biggest absolute error was 1.1 cm, and the relative error was 0.8%. The precision of the system met the request of linear appraisal, and could substitute manual evaluation completely. It also enhanced the efficiency of appraisal.