Objective To explore the isometricity of grafts in ACL(anterior cruciate ligament)recon- struction under bone tunnel shifting condition.Methods Knee specimens from ten fresh frozen cadavers were used. Femoral tunnels of 2 mm were drilled at three points on the medial aspect of the lateral condyle.The first was“anterior bundle point”(located at the 11 o'clock position in the right knee and 1 o'clock position in the left knee).The second was“error point”(located at the place 5 mm anterior and distal to the“anterior bundle point”).The third was“posterior bundle point”(located at the crossing point of the long axis of the ACL attachment and a vertical line drawn across the femoral-tibial contact point with the knee flexed at 90?).Moreover,tibial tunnels of 2 mm were drilled at three points on the tibial plateau.The first was“central point”(located at the center of original insertion of ACL).The second was“5 mm posterior point”,located at the place 5 mm posterior to the“central point”.The third was“10 mm posterior point”,located at the place 10 mm posterior to the“central point”.Changes in distance between each pair of tibial and femoral tunnels were measured during passive knee flexion-extension.Results The anterior-posterior shifting of the tibial tunnel was found to have little influence(P＞0.05)on the isometricity after the femoral tunnel had been chosen.However,the shifting of the femoral tunnel was found to have significant influence(P＜0.01)on the isometricity.Changes in distance related to the“anterior bundle point”led to lengths within the physiologic isometric range.Changes in distance related to the“error point”led to lengthening(ligament stretching)beyond the physiologic isometric range.Changes in distance related to the“posterior bundle point”led to shortening(ligment relaxing)beyond the physiologic isometric range.Conclusion Anterior-posterior shifting of the tibial tunnel between the center of original insertion and posterior edge of inter-tibial eminence area has little influence on the isometricity of grafts in ACL double bundle reconstruction.