Abstract: To improve imaging quality of X-ray digital radiography system, an X-ray flat-panel-detector-based digital radiography system was investigated. Four factors of flat panel detector which degrade image quality, such as random noise, offset, response nonuniformity and defective pixels, were introduced. How they occur and influence imaging quality was analyzed. Corresponding methods for image calibration were put forward to minish and eliminate the influences on image quality. Experimental results indicate that, with the image calibration methods, the influences of above mentioned factors can be removed effectively and the quality of image from flat panel detector can be improved greatly, which has founded a good foundation for succedent image identifying.