This research is to develop an auto optical inspection system for surface mount device light emitting diodes. The principal purpose is to inspect SMD LED for 2D defects which are mixed-material and resin-tearing and for3D defect which is tombstone. In terms with mixed-material inspection, using the count of gradient operator to recognize LED chip. The false alarm rate is 4.29% and misdetection rate is 7.19%. It successfully detects defects with accuracy up to 94.24%. The average computation time is 12.97 ms. In terms of resin-tearing inspection, the research uses the gray scale correlation for SMD LED image registration. The false alarm rate is 5.15% and misdetection rate is 11.34%. The accuracy is up to 91.75%. The average computation time is 10.95 ms. 3D defect continues to use 2D view finder. The advantage of this structure is simple and cost-saving. The investigation which is inspected by the 3D system, comparing with real situation, the average measurement deviation is 4.51%. The average computation time is 8.05 ms. This propose of this system is not only to inspect 2D quickly, precisely and steady, but also to inspect 3D flaws which is hard to detect, and make the wole detective system more artificially-intelligent.