Obiective To study the regularity of three-dimensional displacement in respiration of lung cancer. Methods Af-ter CT scanning, the CT images were transferred into target planning system (TPS) to obtain three-dimensional reconstruc-tion images. Then target drawing and noting of target position, tumor volume, lung function, patient gender, age and weight were performed. The images during the course of inspiration and expiration in simulator were scanned and transferred into TPS by DICOM RT port. At last, the three-dimensional displacement curve of the interested points(X,Y and Z axis) could be obtained. Results The three-dimensional real time displacement curve of lung cancer interested points could be estab-fished by the way of collecting simulator images and drawing interested points. The maximum displacement range of the interested points were 4.2mm in Z-axis(head-foot direction), 3.8ram in X-axis(left-right direction), 2.9ram in Y-axis(ante-rior-posterior direction). Conclusion The three--dimensional real time displacement curve of lung cancer at any point of the target can be established by collecting the dynamic images in simulator and reconstructing of the corresponding images in target planning system through the DICOM RT.