In car license plate recognition systems, license plate location is the precondition of the whole recognition module. Now various methods are used in it, each of which has its own advantage. However, such problems as the quantity in calculation or the low correct location rate are not solved. Edge detection is a common method of license plate location, but edge detection’s quality decides the result of car license image locating finally. Generally, people are accustomed to detecting edges by using gradientbased algorithms and templatebased algorithms, but all of them fail to filter the noise. According to the basic theories and methods of mathematical morphology, this paper puts forward a car license image edge detection operator based on extended mathematical morphology, both the horizontal projection and vertical projection are used to locate the license plate area. The experimental results indicate that the novel proposed algorithm is a better method for car license image edge detecting and noise filtering than the usually used ones, thus realizes the accurate locating of car license plates.