Background Following total knee arthroplasty (TKA) blood loss is a major factor influencing functional recovery and quality of life in patients. The aim of this study was to determine the effect of postoperative leg position on blood loss and functional recovery after TKA.Methods One hundred consecutive patients were enrolled in this prospective randomized study, which with degenerative osteoarthritis of the knee. An equal number of patients were randomly allocated to either flexion or extension groups. In the flexion group, the affected leg was elevated 45° at the hip and with 45° of flexion at the knee, while patients in the extension group had the knee extended fully. Primary outcomes were calculated total blood loss (CBL), hidden blood loss(HBL), intraoperative blood loss(IBL),haemoglobin(HB) level and haematocrit(HCT).Results CBL, HBL, postoperative levels of HB and HCT, drop level of HB and HCT between the two groups after 72 hours were significantly different, with patients in the flexion group experiencing lower blood loss than those in the extension group (P < 0.05).However, there no difference between groups in the postoperative levels of HB and HCT, drop level of HB and HCT at 24 hours. Even though after 1 week range of motion (ROM) was statistical difference in groups, but after 6-week rehabilitation, patients from both groups attained a similar ROM in the knee. Conclusions The results of this study definite that after TKA execute the protocol，maintaining a position with the hip 45°flexion and the knee flexed at 45° prolong 48 hours, is an effective method for reducing blood loss and increasing functional ROM.