This paper presents a CCD camera-based system for slit width measurement of long precision slot dies. The slit width is calculated from the binary image of the slit after positions of the two edges of the slit are determined through a least square linear fitting of the edge data. The resolution of the CCD camera is on the order of sub-microns, which satisfies the requirement of quality control of the slit width. Local slit width can also be obtained because of the small field of view of the CCD camera. The slit width over the entire slot die can be measured enough scanning the CCD camera. The influence of the Z-directional straightness of the scanning stage can be reduced by choosing a proper threshold for binarization of the CCD image. Experimental results have shown that the slit width over the entire length of a 1.4 m long slot die can be measured in 33 seconds.