In recent years, the demands of LED are increasing. In order to test the quality of LEDs, we need LED probes to detect it, so the accuracy and manufacturing methods are attracted more attention by companies. LED probes are ground by people so far. When processing, we often consider the angle and radius of a probe (the radius is between 0.015 mm and 0.03 mm), so it is hard to balance between precision and quality. In this study, we proposed an effective method to measure the angle and radius of a probe. The method is based on Canny edge detection and a curve fitting with iteration. Experimental results show the effectiveness of the proposed method.