Background: During the process of aerobic exercise, there are a lot of jumping and split movements, which can easily cause anterior cruciate ligament (ACL) injury in the knee joint. After undergoing ACL reconstruction (ACLR) surgery, postoperative recovery is crucial. Currently, many methods have been applied, but research on water exercise is still limited. Purpose: This paper aims to understand the role of water exercise in the recovery of athletic ability after ACLR and provide guidance for athletes’ postoperative rehabilitation. Methods: Forty athletes with ACL injuries caused by aerobics practice or competition and undergoing surgery were randomly assigned to either group A or group B. The former received six weeks of a conventional postoperative recovery program, and the latter received six weeks of a water exercise postoperative recovery program. Knee joint range of motion (ROM), swelling value, visual analog scale (VAS) score, knee joint function score, and passive angle reproduction (PAR) were measured before and after the experiment. Results: After six weeks of recovery, the knee ROM was [Formula: see text], the swelling value was [Formula: see text][Formula: see text]cm, the VAS score was [Formula: see text], the Lysholm score was [Formula: see text], and the International Knee Documentation Committee (IKDC) score was [Formula: see text] in group B, which were significantly lower than those before recovery and those in group A ([Formula: see text]). After recovery, the PAR of the affected side was still different from that of the healthy side in the two groups ([Formula: see text]), but the PAR of group B was better than that of group A ([Formula: see text]). Conclusion: Compared to the conventional program, the water exercise-based postoperative recovery program demonstrates better performance in improving knee joint ROM, functionality, and proprioception, and can be used for practical post-ACLR rehabilitation.