Abstract: A flame length measurement method is introduced in this paper. The image is obtained by color matrix CCD and is extracted based on brightness according to the relationship between radiant intensity and the brightness of the flame. The algorithms to determine the flame boundary and compute the flame length are designed based on the extracted image. Finally, the test experiment is evaluated with the candle in the laboratory. The brightness image is extracted and filtered by Matlab. The actual flame length is obtained in Visual C#. The method is more convenient and simpler than traditional manual measurement.