The invention discloses an automatic detecting and analyzing method and system for crosswalk lines. The automatic detecting and analyzing method for crosswalk lines includes that inputting images of street scene, dividing the images into a training group and a testing group, and using the training group to train a classifier for detecting crosswalk lines; for example, using the classifier to detect and identify the crosswalk lines of the images of the testing group, and eliminating the false detection through post-treatment; using the classifier to detect and identify the crosswalk lines of the images of the training group, and eliminating the false detection through post-treatment; counting the detected results according to the identified results of the images of the testing group of the step 4 and the identified results of the images of the training group of the step 5, for any image of the testing group or any image of the training group, accumulating the pixels in the rectangle of each identified result according to the difference between the transverse coordinates, using the pixels corresponding to the transverse coordinate values as the total number of the crosswalk lines, drawing a histogram and extracting characteristics, and training a neural network model for analyzing fouling degree to analyze the fouling degree of the crosswalk lines.