Objective To analyze the imaging characteristics of thoracic LDRD(Low-dose directly Digital Radiographic Device) and its artifacts.Methods 188 patients were performed with LDRD and common thoracic X-ray film respectively in our hospital during two weeks.Results Among the 188 cases,1.60%(3/188) showed thoracic motion artifacts.46.8%(88/188) appeared as tentorial prominence along left heart edge and 2.6%(5/188) along the right one.1 artifact was in aorta-pulmonary artery window(0.53%).Conclusion(1)Less than 0.5 should be taken as reference in podoid enlargement diagnosis.(2)Pseudomorph from heart motion may result from cardio-phase,cardiac contraction,heart rate,arrhythmia,local abnormal pulse of left heart edge,different enlarged velocity of cardiac cavity during heart beat,etc.(3)The motion artifacts in thoracic LDRD has no important influence in clinical diagnosis and therapy.