Objective To develop a remote self-mutual-aid functional assessment system based on the knee society score (KSS), and to verify its effectiveness for patients after total knee arthroplasty (TKA). Methods Ten TKA patients were selected, and their functional status was recorded preoperatively, on the day of surgery (0 d), on postoperative 4th and 30th day using the functional assessment system. The system automatically calculated the patient data including KSS score, total range of flexion, flexion contracture, extension lag, knee alignment, pain, and knee stability. Results The results of manual KSS scores by physicians based on experience were compared with the result of KSS scores assessed by the system, and there was no statistically significant difference between the scores, indicating an agreement. Conclusions The KSS scores collected by the remote self-mutual-aid functional assessment system are consistent with the results assessed by clinicians, and the system provides a reliable and convenient method for home assessment and remote rehabilitation guidance for patients after TKA.