Objective To establish a three-dimensional finite element model of mandible with dental implants for immediate loading, and to analyze stress distribution in the bone around the dental implants with different implant diameter. Methods Three-dimensional finite element model of thread dental implants with immediate loading were constructed using CT scanning and USIS (Universal Surgical Integration System)software developed by ourselves, which including different diameter implants for 3.3 mm、 4.1 mm、 4.8 mm, respectively. The value of Von Mises stress、 strain of implant-bone interface were obtained and analyzed with ANSYS, when the dental implants were loaded with vertical、 buccolingual force of 150 N. Results When loaded with vertical force, the Von Mises stress concentration appeared on the neck of implants, and Von Mises strain were concentrated on the buccal side of the bottom of implants; the peak value of Von Mises stress on the neck of implant in the implant-bone interface for the above three different diameters were 25 Mpa、 17.6 Mpa、 11.6 Mpa and the strain of them were 1 853 με、1 303 με、1 293 με, respectively. When loaded with buccolingual force, the values of both Von Mises stress and strain increased apparently and the concentrations all appeared around the lingual side on the neck of implants , the corresponding peak values for the above three different diameters were 131.1 Mpa、 78.7 Mpa、 68.1 Mpa and the strain of them were 9 622 με、5 892 με、5 816 με,respectively. Conclusion With the addition of the dental implants diameter , the stress and strain on the bone around implants all decreased and it was remarkable especially when the diameter increased from 3.3 mm to 4.1 mm. It shows that the dimension of dental implants with immediate loading would at least be 10 mm×1 4.1 mm, and should avoid load with un-axial strength as possible as it can.