Abstract: A new automatic target detection algorithm is proposed to detect infrared ship in complex sea-sky background.To procure the potential target regions,in the method,a combined high-pass filter in frequency domain is designed to filter original image.Afterwards,a scale-adaptive local threshold segmentation method is presented for extracting integral possible ship based on the potential target regions.Waterline detection is employed to distinguish correct ship finally.As the new method does not depend on the information of sea-sky line position and high brightness ship chimney or engine,its performance has been improved greatly.Experimental results indicate that the proposed method not only demonstrates reliable target detection capability for infrared ship in complex sea-sky background,but also shows efficiency.