Objective To develop a remote self-mutual-aid functional assessment system based on the Knee Society Score (KSS), and to verify its effectiveness in home assessment of patients after total knee arthroplasty (TKA). Methods Ten postoperative knee replacement patients were selected and their functional status was recorded preoperatively, on the day of surgery, on postoperative day 4 and on postoperative day 30 using the functional assessment system. The system automatically calculates patient data including KSS score, total range of flexion, flexion contracture, extension lag, knee alignment, pain, and knee stability. Results The results of the functional assessment system were compared with those of the clinician evaluation.There was no statistical significance (p < 0.326) between the results of the manual KSS scoring by the doctor with experience and the KSS scoring by the system evaluation. Conclusion 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.