Objective: To compare the stress distribution on the temporomandibular joint (TMJ) before maxillary expansion and when expander loading on the maxillary by using the three-dimensional finite element method. Methods: The finite element models before maxillary expansion and when expander loading on the maxillary were reconstructed by image data of CBCT from a patient with maxillary transverse deficiency. The same muscle force and boundary constraint were applied on the two models, and then evaluate the von Mises, the maximum principal stress and the minimum principal stress on the mandibular condylar, joint disc and glenoid fossa. Results: The equivalent stress of TMJ was mainly distributed in the anterior mandibular ramus, the anterior of condyle, the middle of articular disc and the top of articular fossa. Compared with before expansion, there is no significant different of the stress distribution on the TMJ when expander loading on the maxillary. However, the stress of the TMJ was larger than before expansion, there is no significant stress concentration. The stress distribution of condyle and disc are more lateral and anterior. The posterior of the condyle shows a wider distribution of maximum principal stress. Conclusion: The orthopedic force generated by maxillary expander can increase the stress value of temporomandibular joint and stimulate tissue reconstruction of condyle. In clinical practice, the patients with maxillary transverse deficiency should be treated with appropriate means of maxillary expansion.