Abstract: The present invention disclosed a method and system inspecting cotton web homogeneity by a digital image processing technique, in particular, for an on-line cotton web homogeneity test. It uses optical principles in conjunction with a charge coupled device type camera to find a theoretical equation indicating the correlation between the transmittance of cotton webs and basic weights (weights per unit area). Next, the invention makes use of a numerical analysis method to find the optimal approximation equation representing a relationship between measured transmittance and basic weights of cotton webs. When executing an on-line inspection, a system according to the invention detects the transmittance of cotton webs by means of the computer controlled visual device and then calculates correlated data of cotton web homogeneity variations according to the approximation equation acquired previously.