Objective To investigatey the changes of tibial and femoral bone tunnels and the influence of residual length after old anterior cruciate ligament injury and fresh injury，and to evaluate its clinical efficacy. Methods A total of 320 patients with anterior cruciate ligament injury admitted to our hospital from January 2020 to January 2021 were selected and assigned to fresh injury group（≤ 3 months after injury，n = 160）and old injury group（> 3 months after injury，n = 160 ）. CT was performed at different time periods. The changes of tibial and femoral bone tunnels in the two groups were measured，and the IKDC，Lysholm and Tenger scores of the knee joint，the recovery of knee proprioception and the healing of tendon and bone by nuclear magnetic resonance were monitored. Results The residual length of the fresh injury group was significantly better than that of the old injury group（P < 0.05）. At 6 months after operation ，the tibial and femoral bone tunnels of the two groups were enlarged. The expansion of the femoral bone tunnel in the fresh injury group was smaller than that of the old injury group. There was a statistical difference between the two groups（P < 0.05），but there was no statistical difference between the two groups（P > 0.05）. At 1 year after operation，the tibial and femoral bone tunnels were enlarged at the same time. The expansion of the bone tunnel in the fresh injury group was significantly smaller than that in the old injury group. There was a statistical difference between the groups（P < 0.05）. Compared with the old injury group，the IKDC，Lysholm and Tenger scores of the fresh injury group were significantly better than those of the old injury group（P < 0.05）. There was no significant difference in knee proprioception between the two groups at 6 months after operation（P > 0.05）. At 12 months after operation，the fresh injury group was significantly better than the old injury group. There was significant difference between the two groups（P < 0.05）. Conclusion Early anterior cruciate ligament reconstruction（≤ 3 months）could better preserve the stump，prevent the expansion of the tibial femoral tunnel and restore knee function.