Objective To investigate the effect of thickness and elastic modulus of anterior talofibular ligament (ATFL) on ankle stability, and provide references for ankle instability diagnosis. Methods The threedimensional (3D) model of ankle joint was established. By changing the thickness and elastic modulus of ATFL, the ankle anteroposterior stiffness (AAS) was calculated and used as a quantitative indicator to assess ankle stability. Results AAS changed significantly when the thickness of ATFL was in the range of 0. 78 mm to 2. 31 mm, and such relationship was in an S-shaped curve. AAS significantly increased with the elastic modulus of ligament increasing, when the elastic modulus of ATFL was in the range of 60 MPa to 400 MPa. Conclusions Both the thickness and elastic modulus of ATFL will influence the stability of ankle joint.