OBJECTIVES: To compare water-based treadmill walking training with land-based treadmill walking training following anterior cruciate ligament (ACL) reconstruction. DESIGN: Prospective, randomised, single-blind clinical trial. SETTING: Single-centre study. PARTICIPANTS: Sixty patients undergoing rehabilitation following ACL reconstruction were assigned at random into two groups. INTERVENTIONS: Patients in the water-based training group (WBG) underwent treadmill training in water, and patients in the land-based training group (LBG) underwent treadmill training on land. MAIN OUTCOME MEASURES: Muscle strength was evaluated using the ratio of peak torque to body weight (PT/BW) before and after 3 weeks of training. RESULTS: After 3 weeks of training, both groups had significantly higher PT/BW ratios, passive position sense (PAPS) and Lysholm scores compared with pre-treatment levels. In the affected leg, the PT/BW ratio for the knee extensor muscles, PAPS and Lysholm scores showed significantly greater improvement in the WBG than in the LBG. No significant differences in the PT/BW ratio, single leg balance index and stability limit index of the knee flexor muscles at different angular velocities were seen between the two groups. CONCLUSION: The results suggest that water-based walking exercise could lead to greater improvements in extensor muscle strength, proprioception and knee performance compared with land-based training following ACL reconstruction. CLINICAL TRIAL REGISTRATION NUMBER: ChiCTR1900025930.