Objective：To investigate the effect of residual flexion deformity（FD）to a certain degree during total knee arthroplasty （TKA）on the efficacy in patients with severe FD associated with knee osteoarthritis. Methods：A retrospective analysis was conducted at the First Affiliated Hospital of Nanjing Medical University on the 52 patients with severe FD（＞30°）treated based on the concept of completely correcting FD（within 5°）from October 2013 to September 2017，referred to as the intraoperatively completely -extended group（n=52），and the 43 patients treated based on the concept of appropriately retaining a certain degree of FD（5°-10°）from October 2017 to September 2021，referred to as the intraoperatively incompletely -extended group（n=43）. The operation time，intraoperative blood loss，postoperative lower limb swelling，and the incidence of postoperative complications were recorded. The hospital for special surgery（HSS）score，activities of daily living scale（ADLs），and visual analogue scale（VAS）were also to compare the differences between the two groups. Results：All patients successfully completed the surgery，and were followed up for（35.85±1.99）months（range 33-39 months）. Patients in the intraoperatively incompletely-extended group had shorter surgical time（P=0.001），less operative blood loss（P ＜ 0.001），and had less postoperative lower limb swelling（P ＜ 0.001）. At 3 months post-surgery，patients in the incompletely-extended group had greater residual FD（P=0.038）but less pain（P=0.031）than those in the completely-extended group. No significant differences were found in postoperative HSS and ADLs scores between the two groups. At 6，12，24，and 36 months post-surgery，there were no statistically significant differences in residual FD，HSS，ADLs，and VAS between the two groups. The improvement in HSS scores also showed difference at 3- 6 months post - surgery（P=0.004），but not at other time points. The incidence of deep vein thrombosis（DVT）was lower in the completely -extended group（P=0.048），but there was no statistical difference in the incidence of medium-term and long-term complications between the two groups. Conclusion：In the treatment of knee osteoarthritis with severe FD， retaining soft tissue to a limited extent and appropriately retaining a certain degree of FD（5°-10°）during TKA does not affect the recovery of knee mobility and function and is associated with a lower incidence of DVT.