Eight kinds of reheated oils（genetically modified soybean oil，non genetically modified soybean oil，sunflower oil，peanut oil，corn oil，safflower oil，cooking oil，olive oil） were identified by fourier transform infrared spectroscopy（FT-IR）.Unsaturated degree of unsaturated fatty acids（e.g，linoleic acid and linolenic acid） in cooking oil decreased and saturated fatty acids（e.g.palmitic acid and stearic acid） increased under the condition of high temperature reheating，while the cis fatty acids were also changed to be trans fatty acids.The absorption of the peak at 3 009，988，966 cm-1 were selected as characteristic absorption peak of the alkene and trans structure by second order derivative spectrophotometry.This method，with the advantages of simplicity，small dosage and rapidness for quality analysis of reheated oil in market screening，could be used as the theoretical evidence for determination of waste oil.