In order to study the possibility of monitoring the rape canopy’ nutrition information based on computer-vision technology in the outdoor ray, the computer-vision system was designed, and the images of the rape canopy were got and segmented. Through the statistical analysis of stepwise regression, the perfect models of chlorophyll content, total-N content, and C/N ratio were found and have a good predictive ability. The result showed that it is possible to estimate the physiological indexes of rape canopy, including chlorophyll content, total-N content, and C/N ratio, with digital camera under the conditions of field natural light.