Aiming at the detection of the ship on sea surface under the ocean background,a fast detecting algorithm for ships on sea surface is proposed. The high frequency component of Gaussian pyramid in the image is calculated,and three layer dimension reducing images of Laplacian pyramid are obtained. Compared with the original image,the dimensionality of the second layer dimension reducing image is reduced by 16 times. After that,based on the improved Sobel edge detection in dimension reducing image,the contrast of ships is enhanced and the region of interest is highlighted to achieve rapid detection. The experiment results show that this method has certain robustness and can achieve the fast detection of ships on sea surface.