Abstract: Surface defects occurring in strip and their formation mechanism had been investigated. By the means of key process data analysis and SEM observation,it was found that the morphologies of the defects are similar,but the causes are different. The structure characteristic of layered defects induced by exogenous inclusions is that many particles containing F、Na、Mg、Si and other elements combined with iron oxide/inclusion co-exist layer distribute along the rolling direction continuously. The layered defects of thin gauge cold rolled strip possess a smooth interlayer,which is caused by the improper process parameters adoption. Scratch characteristic is significant near the silver defects,and no oxidant or inclusions are found. This findings provide a new way for the analysis of strip surface defects.