Objective:To discuss the factors for affecting image quality of flat panel detector on modified DR and the solution.Methods: We observed disturbed condition of image on display by changing spatial resolution of flat panel detector, grid and display under a certain exposure condition, and observed improvement condition of image quality by changing exposure condition.Results: The variation of spatial resolution of flat panel detector, grid and display could affect image quality directly in DR. The variation of exposure dose could also affect resolution and contrast of image within limits.Conclusion: When taking radiography by flat panel detector, if the spatial resolution of image sections were close, the image would form wave-shape- stripe disturbance with strong regularity and high distinguishability; if the deviation of spatial frequency was large or be in multiple relationship, there would be no wave-shape- stripe on image, or the disturbance was inconspicuous. At the same time, choosing suitable radiography condition also showed certain effect to improve image quality.