A method and device for detecting a spliced banknote. Edge detection and enhancement processing are performed, by using a horizontal Sobel operator and a vertical Sobel operator, on an image of an area to be detected, to obtain a first image and a second image; projection processing is performed on the first image and the second image to obtain a horizontal grayscale projected curve and a vertical grayscale projected curve; whether the projection result of the horizontal grayscale projected curve and the vertical grayscale projected curve meets a requirement of a normal banknote is determined, so as to identify whether a banknote is a spliced banknote. The invention can accurately detect spliced banknotes and eliminates the need to perform binarization processing and Hough transform processing on a banknote image, reducing detection complexity of spliced banknotes, and improving detection efficiency.