Objective To evaluates the effects of cross-balance training on knee function, dynamic balance, and rectus femoris (RF) activation in patients after anterior cruciate ligament reconstruction (ACLR). Methods Forty ACLR patients at 5–6 week after operation were randomly divided into experimental group and control group. The experimental group received the cross-balance training on the basis of the standard rehabilitation, while the control group received only standard rehabilitation. Knee function was assessed with the Lysholm score, dynamic balance, and root mean square (RMS) of RF surface electromyography. The correlation between RMS and dynamic balance was also examined. Results After intervention, the Lysholm score of the experimental group was significantly higher than that of the control group (P<0.01). Regarding balance function, both the gait line length and single support line length of the experimental group were significantly greater than those of the control group (P<0.01). Conversely, mediolateral displacement of the experimental group was significantly lower than that of the control group (P<0.01). Furthermore, the RF RMS of the experimental group was significantly larger than that of the control group (P<0.01). The RF RMS was positively correlated with the gait line length and single support line length, whereas it was negatively correlated with the mediolateral displacement (P<0.05). Conclusions Cross-balance training significantly enhances knee function, dynamic balance, and RF activation in post-ACLR patients, supports the theory of cross-education. This study shows that cross-balance training has certain application values in ACL postoperative rehabilitation.