Background <p>Anterior cruciate ligament (ACL) injury affects individuals, and successful ACL helps patients return to an active lifestyle. This study compared the clinical effects of two treatment schemes of retention length ≥ 1/2 and &lt; 1/2 of ACL stump in patients under reconstruction with peroneus longus tendon (PLT).</p> Methods <p>A total of 34 patients with ACL injury of knee joint treated by unilateral ACL reconstruction with PLT were recruited in this study. They were divided into N1 (retention length of ACL stump ≥ 1/2) and N2 (retention length of ACL stump &lt; 1/2) groups (<i>n</i> = 17 in each group). The knee joint proprioceptive threshold of passive motor perception was used to evaluate recovery of proprioception. The international knee documentation committee (IKDC) score, Lysholm score, and Tegner activity score (TAS) were used to evaluate knee joint functions. Lachman test, anterior drawer test (ADT), and pivot shift test (PST) were used to evaluate the stability of knee joint. Single-legged hop test and return-to-sport ratio were used to evaluate the movement ability.</p> Results <p>In 6th month and 12th month after operation, the passive motor perception threshold in N1 group was better than than that in N2 group (<i>p</i> &lt; 0.05). In 12th month after the operation, the return-to-sport ratio in N1 group was increased compared to the N2 group (<i>p</i> &lt; 0.05). There were no significant differences in results of IKDC score, Lysholm score, TAS, Lachman test, ADT, or PST between the two groups in 6th month and 12th month after the operation (<i>p</i> &gt; 0.05). In addition, no significant difference was found in the single-legged hop test between the two groups in the 12th month after operation (<i>p</i> &gt; 0.05).</p> Conclusion <p>During ACL reconstruction with PLT, treatment strategy of ACL stump retention length ≥ 1/2 is more effective than treatment strategy of length &lt; 1/2 for patients with ACL injury of the knee joint.</p>