Objective:To study stress distribution of All-on-Four distal implants with different tilt angles and lengths on edentulous maxilla using the three-dimensional finite element method. Methods:A female patient with edentulous maxilla was selected. After data collecting and three-dimensional reconstruction,a three-dimensional finite element model of edentulous maxilla with All-on-Four implant restoration was established. According to the tilt angles and lengths of the distal implants,there were four groups:Group A:30°,11.5 mm; Group B:30°,13 mm; Group C:45°,11.5 mm; Group:D 45°,13 mm. 100 N vertical static force was loaded on the first premolar,the second premolar and the first molar to simulate chewing, respectively Equivalent stress values of implants on the edentulous maxilla model were calculated using ABAQUS software. Results:Under the vertical static load,stress concentration was found around the implant neck in the cortical bone area. With the increase of the distal implant length,the stress decreased slowly in all regions. With the tilt angle of distal implant increasing,the distribution of stress became more dispersed and the stress in implant neck and apical areas significantly reduced. Conclusion:The stress distribution and magnitude of distal implant did not change significantly with the increase of the implant length,while the implant tilt angle of 45° was more favorable for stress dispersion than the implant tilt angle of 30°.