Compare the isokinetic muscle strength indicators and surface electromyography (sEMG) signals of the healthy side lower limb of non-contact anterior cruciate ligament injury (ACLD) patients in the acute phase with those of healthy individuals to provide theoretical basis for the prevention of secondary ACL rupture in the healthy side lower limb of ACLD patients. The method was to divide the 21 patients with ACLD in the acute phase into the ACLD group and divide the 21 healthy individuals into the control group. Both groups of experimental subjects were subjected to isokinetic muscle strength tests for hip flexion, extension, adduction, abduction, and knee flexion, and electromyography signals of the vastus medialis, vastus lateralis, semitendinosus, biceps femoris, and gluteus maximus were collected during the single-leg jumping action. The differences between the two groups in relative peak torque, antagonist muscle ratio, root mean square amplitude, and co-contraction index were analyzed by independent sample t-test. The results showed that the extension of the knee (P=0.040) and hip flexion strength (P=0.041) were lower in the healthy side lower limb of ACLD patients; in the single-leg landing action, there was lower activation of the vastus medialis muscle in the pre-activation phase (P=0.014), lower activation of the vastus medialis (P=0.010) and gluteus maximus (P=0.002) in the reaction phase, and also lower co-activation level of the biceps femoris-semitendinosus (BF-ST) (P=0.020). The function of the healthy side lower limb of ACLD patients showed changes in the early stage of injury, which may suggest the reason why ACLD patients face a greater risk of contralateral lower limb injury.