Because of the shortage of rule gap measurement for light guide plate (LGP) warpage degree, image definition criterion of quality indexing is present based on single CCD camera. The detection paper and LGP are respectively arranged on the camera detection device platform, located by X-and Y -axes driving unit and focused by Z-axis driving unit firstly, different image definition criterion peaks of edge detection evaluation function are obtained in the middle surface of LGP bottom and surface. Finally, different edge detection algorithms are compared under different situations. Results show that the algorithm has good repetition and can meet the online, untouched detection needs.