Considering difficulties in performing automatic recognition for manhole covers under complex background,this paper proposed a Hough transform algorithm to locating the possible positions of the manhole covers based on features of ellipse geometry extracting from images by Mobile Mapping Systems(MMS).Firstly,the original images need to be preprocessed by image enhancement,edge detection,and morphological closing operation.Then the processed image was filled,the image noises with very small areas were removed,and the remaining blocks were identified.A ratio of the ellipse area to its outer rectangle area was calculated as the threshold value to eliminate large amount of image noises so as to obtain the maximum likely positions of manhole covers.Finally,the Hough transform was used to identify the accurate locations of the manhole covers.Experiments with fifty images have showed that the proposed algorithm can achieve a 88%accuracy of identifying the manhole covers correctly,automatically and quickly.