Objective To investigate the feasibility of simulating the deformation and displacement of lung tumors by simulating the motion of lung tumors during respiration using finite element method (FEM). Methods The CAD (computer-aided design) surfaces of the lung at multiple inhalation phases were reconstructed from 4D CT images of a patient with lung tumor. The finite element model was established according to the surface at the beginning of inhalation. Distributed surface loads were defined by the differences between each individual surface and the surface at the beginning of inhalation, and applied to the surface of the model. The motion and deformation of lung tumors were then simulated using FEM within the inhalation cycle. Results The numerical simulation indicated that the estimated errors for the lung and the tumor’s motion and deformation were less than 2 mm and 1 mm, respectively. The use of linear elastic relationship for tumor with elastic modulus of 50 kPa could achieve higher precision in simulation. Conclusions The deformation of lung and the displacement of lung tumor are possible to be simulated accurately by FEM. This research provides references for the X-ray free lung tumor tracking method based on numerical simulation.