Calculation of confidence level for image matching is introduced, which is based on the assumption that image pixels are independent each other and no spatial correlation is in the scene. A large number of tests on the real sensed image has been implemented to estimate the accuracy of calculation. It shows that the value of the confidence level can be used to judge the credibility of matching result, especially when the confidence level is close to 1.0 or less than 0.5, however the matching position is uncertainty when the confidence level is higher than 0.5 and less than 0.99. Further more, how to improve the estimation accuracy of the confidence level is discussed.