Abstract: Objective： To evaluate the root canal working length measurement on dental digital radiographs, in order to provide reference date for the clinical application. Methods： According to experimental criteria, 99 extracted anterior teeth were collected in this study. After opening the pulp chamber, the gutta percha point was fixed in the root canals, with its tip reached the anatomical apical foramens first and then retreated a little. By imitated X-ray parallel techniques, the distance from the top of gutta percha to the apex was measured in the digital images with the software, and compared with the actual length of gutta percha on the extracted teeth through the SPSS 17.0 software. And these data represented the distance from anatomical apical foramens to apex. Results：Imitated X-ray parallel techniques resulted in almost no magnification. There was no significant difference between the distances from anatomical apical foramen to apex on both X-ray images and the extracted teeth (P>0.05). The anatomical apical foramens were both over 50% around apex. The difference between the anatomical apical foramen to apex was longer in the side ones than the vertical ones (P<0.01). Conclusions：Direct digital radiography system is reliable in the measurement of root canal working length, but the distance from foramina to the anatomic root apex should be taken into consideration.