A precise license plate locating algorithm was proposed combined with the mathematical morphology to solve the problems of existing locating algorithms such as low locating rate and slow speed. The algorithm was based on edge detection and color information. First color-image was preprocessed with grayscaling, smoothing and gray stretching and so on, then vertical edges detection and binarization were implemented on the image. After that linear filtering algorithm was adopted to filter disturbing edge lines, and up-down plate edges were located utilizing the characteristic of plate area′s variety in gray scales. Isolated points of the up-down edges located plate were filtered by using a point density filtering algorithm, then the plate area was located coarsely by finding connected components with adopting the mathematical morphology. Finally the plate was precisely located through color segmentation in HSV space and incline rectification. The experimental results show that this algorithm can locate the plate precisely and quickly.