1. An alignment film detecting device realized by a computer for detecting alignment grooves formed on an alignment film of a substrate, the alignment film detecting device comprising: an imaging circuit configured to obtain a grey scale stripe image of the alignment grooves on the alignment film of the substrate; and an image processing circuit configured to determine whether there is a defect in the alignment grooves on the alignment film through measuring depth values or width values of respective alignment grooves on the alignment film of the substrate by conducting an identification process on the grey scale stripe image based on the grey scale stripe image, and connected to the imaging circuit, wherein the imaging circuit comprises: a ray source configured to generate rays that are to be transmitted through the substrate comprising the alignment film; and a receiving circuit arranged to be opposite to a position of the ray source relative to the substrate, and configured to receive the rays having been transmitted through the substrate and generate a grey scale stripe image, wherein the grey scale stripe image comprises first grey scale image regions corresponding to the alignment grooves on the alignment film and second grey scale image regions corresponding to portions between every two neighboring ones of the alignment grooves, and the first grey scale image regions and the second grey scale image regions are arranged alternately.