Abstract: Aiming at the drawbacks of the traditional way for cocoon evaluation,a measurement method for cocoon superficial area was advanced based on the technology of machine vision.It employed the system of machine vision to obtain the cocoon image,advanced segmentation using the way of Otsu for the image character of gray value distribution.Assuming that cocoon is ellipsoid,cocoon superficial area can be calculated by the long axis and short axis of cocoon region.Using the value of elliptical long axis and short axis determined by minimum enclosing rectangle based on cocoon edge image,the cocoon superficial area at discretional vertiginous angle can be measured.The experiment result indicated that the method is effectively,offering a basis for scientific evaluation of cocoon.