Atmospheric visibility has an important impact on aviation, navigation, land transportation, military activities and so on.The image method based visibility measurement is a new method, which has a certain degree of error in the measurement of visibility because of the errors of the imaging brightness and the dynamic range.The relative errors of visibility measurement caused by target brightness gain error, target brightness zero error, sky background brightness gain error and sky background brightness zero error are analyzed in detail.The total relative errors of visibility caused by the above four errors are obtained.The feasibility and validity of the image method based visibility measurement are verified.