Objective: To analyze the effectiveness of a modified knee joint functional exercise method combined with a goniometer in patients after joint replacement. Methods: Sixty patients who underwent orthopedic knee replacement were divided into two groups: a control group (n = 30, conventional intervention) and an intervention group (n = 30, modified knee functional exercise method combined with a goniometer). Postoperative knee function (Knee Society Score, KSS), compliance with functional exercises, and quality of life were evaluated and compared between the two groups. Results: Before the intervention, as well as two days post-operation and on the day of discharge, there were no significant differences in KSS scores between the two groups. However, at 2 weeks, 3 weeks, 1 month, 3 months, and 6 months post-operation, the intervention group showed significantly higher KSS scores compared to the control group (P < 0.05). The compliance rate of knee joint function exercise in the intervention group was significantly higher (P<0.05). After intervention, the PF, GH, VT, and MH dimensions of quality-of-life scores in the intervention group were higher than those before intervention and higher than those in the control group (P<0.05). Conclusion: The modified knee functional exercise method combined with an goniometer effectively improves knee function, enhances training compliance, and improves the quality of life in patients following joint replacement.