Abstract: In order to improve the detectivity of defects in radiographic inspection of welds, the influence of the density of radiographs,defect characteristics and weld state on the detectivity has been systematically studied according to the image result of defects.The results showed that the optimum detectivity can be obtained when the density of radiographs ranges from 2.0 to 2.5. The detectivity for annealed welds is better if compared with that for as-welded welds, and the detectivity for normalized welds is the best.