Abstract [Objective] To explore the risk factors related to failure of proximal femoral nail anti-rotation (PFNA) for intertrochanteric fractures of femur in the elderly.[Methods] A retrospective study was conducted on 148 patients who were old equal to or more than 80 years with femoral intertrochanteric fracture in our department from January 2015 to January 2019.According to whether the internal fixation failed, the patients were divided into failure group and effective group.The clinical outcomes were compared between the two groups. [Results] A total of 148 patients were followed up for an average of 13.2 months ( range: 12-18 months ), . Internal fixation failure was observed in 27 cases(3-12 months after surgery) and the failure rate was18.24% ,type A1-2 12 cases, type A3 15 cases,helical blade loose screw 8 cases,varus hip malformation 11 cases,femur neck cut-out 6 cases,blade penetration into the hip joint 2 cases, breakage of implant 1 cases, Statistical analysis showed that on tip-apex distance（OR=21.087，P<0.001）, fracture reduction（OR=9.943，P= 0.003）, internal position of spiral blade in the femoral head（OR=6.077，P= 0.020）, fracture stability（OR=21.087，P= 0.012） and unstable lateral wall（OR=12.361，P= 0.002）were independent risk factors for failure of intertrochanteric fractures of femur.[Conclusion] Destruction of lateral wall, unstable fractures, poor reduction of intraoperative fractures, poor position of spiral blades, and TAD >25mm are major causes of failure after PFNA internal fixation., which should be paid attention to in clinical treatment.