As many cases such as skin needling and rough edge occur in edge extraction of infrared image by using traditional Canny operator,an improved edge detection algorithm is proposed.Firstly,principle operator obtained by PCA replaced Sobel operator,and non-max suppression method based on second derivatives are used to thin the edge.At last “reference white” method is used to extract final edge through setting threshold.Simulation results show that the proposed method can get smoother edge,especially for arch edge,compared with Canny operator.