This presentation introduces a novel model for analyzing the optical interface performance degradation due to scratches on optical fiber endface. The model indicates that the contribution to the return loss of a scratch is determined by its size, location and its relative reflectivity, which is defined as the ratio of the average reflectivity of the scratch to the base reflectivity of the defectless endface. Based on this new model, the effects on return loss are analyzed for scratches of various numbers, different sizes, with different relative reflectivities, and at different locations. This quantified analysis provides a solid base to establish the specifications of inspection criteria of optical interface. With the new model, the relative reflectivity of a scratch was tested, and estimations of the return loss of scratched connectors were performed, which were in good agreement with measurement results.