The invention relates to a method for measuring tunnel lining cracks. The method comprises the following steps of: acquiring an image of a crack by a
digital camera and measuring the acquisition distance by a
laser ranger; selecting an area needing to be measured from the acquired image so as to prevent
processing deviation due to excessively big picture and relatively
small target crack, and changing the selected area into a gray image; determining a threshold for the selected gray image and performing binarization image division to obtain a target area; extracting a
white area only comprising the crack from the target area; extracting the border of the crack to obtain a border graph; calculating the pixel width of the crack by a
minimum distance method; and obtaining the actual width of the crack according to a predetermined calibration proportion between the actual pixel size and the photographing distance. The method has the advantages of low cost, high speed, convenient carrying and high
measurement precision.