Objective The three-dimensional finite element model of mandible with dental implants for immediate loading was established to analyze stress distribution of bone around the dental implants with different implant length. Method Five three-dimensional finite element models of thread dental implants with immediate loading were constructed using CT scanning and USIS(Universal Surgical Integration System)software developed by ourselves. Each of them included different length implants which was 6 mm、8 mm、10 mm、12 mm、14 mm respectively. The values of Von Mises stress and strain at implant-bone interface were calculated with the software of ANSYS, when the dental implants were loaded with vertical、buccolingual force of 150 N. Result The values of Von Mises stress and strain on the bone around implants all decreased with the length of dental implants increased. With the length increased from 6 mm to 8 mm, the value of Von Mises stress at implant-bone interface reduced remarkably, especially when the dental implants were loaded with buccolingual force. However, when the length increased from 8 mm to 10 mm, from 10 mm to 12 mm and from 12 mm to 14 mm, the values of Von Mises stress decreased unapparent. The value of Von Mises stress at implant-bone interface also reduced obviously with the length increased from 6 mm to 8 mm. Conclusions With the length of dental implants increased, the value of stress at implant-bone interface decreased, which showed a negative correlation in between. But the increase only appears apparently when the length of dental implants added from 6 mm to 8 mm. It suggests that we should choose sufficient longer implants in clinical treatment and avoid use the implant of 6mm length if possible.