Abstract: Through the analysis of the CCD image system,a noise measurement method based on relative measurement theory is provided.This noise measurement method can compute the CCD image system noise continually at real time through the correlation value of two images taken at the same scene and same conditions.The result of the test was shown that the relative noise measurement method can get over or minish the environmental influences and the measuring process of the method is simple and easy to do so that it can become the important and available noise measurement approach especially for the cooling CCD image system.