Objective To investigate the differences in stress distribution at the bone-implant interface of dental implants with different length-diameter ratios, so as to provide references for the design of novel dental implants. Methods The three-dimensional finite element model of mandible was established using Geomagic studio, SolidWorks and ANSYS Workbench software. The mandibular molars were applied with different vertical or oblique forces, to compare and analyze stress distributions on dental implants and the surrounding bone tissues. Results Under the same length-diameter ratio, the maximum peak equivalent stress of implant under oblique loading was significantly higher than that under vertical loading. The Von Mises stresses of implants in Group A and Group B occurred in the neck under oblique and vertical loading. Under oblique loading, the implant stress variation in Group A and Group B was 144.74-374.67 MPa and 161.52-475.38 MPa, respectively. Under vertical loading, the implant stress variation in Group A and Group B was 101.28-187.40 MPa and 110.08-210.32 MPa, respectively. The maximum Von Mises stress of Group A was significantly smaller than that of Group B. Conclusions Dentists should focus on a length-diameter ratio of 2.67 to select the standard implants, and the jawbone quality of patients should be taken into full account.