Abstract: Objective　To compare the influence of implants with different diameters and lengths on the stress distribution of implant - bone interface. Methods　According to the different lengths and diameters of the implant,, fully three-dimensional finite element model was established. The 3 I implant system used as reference, 3D entity model including the implant, corresponding abutment and dental crowns was drawn with Solidworks 3D cartography software. The group for size analysis consisted of 16 implant model with the cross combination of the different lengths which were set to 8 mm, 10 mm, 12 mm, 14 mm and the different diameters set to 3.5 mm, 4.0 mm, 3.5 mm, 5.0 mm. Take vertical and oblique loading on each model, and compare Von Mises stress distribution and the trend of stress changes of each model with Ansys Workbench13.0. Results Under each loading, the Von Mises stress of implant-bone interface in all models concentrated in the cortical bone around the neck of implant and cancellous bone area of the root tip. With the increase of implant length, stress concentration in the cancellous bone area of the root tip slowly declined while with the increase of the diameter, the stress concentration decreased significantly. Conclusion　Both diameter and length have an influence on the stress concentration of implant - bone interface. The longer the diameter and the length, the smaller the stress concentration. Compared with length, diameter has a more significant influence.