Objective To analyze the failure factors of proximal femoral nail antirotation (PFNA) in the treatment of geriatric intertrochanteric fractures. Methods The clinical data of 136 cases of intertrochanteric fracture treated with PFNA internal fixation between May 2015 and June 2017 were retrospectively analyzed. There were 106 males and 30 females, aged from 60 to 80 years, with an average age of 75.5 years. According to Evans-Jensen classification, there were 45 cases of type Ⅰ, 50 cases of type Ⅱ, 23 cases of type Ⅲ, 13 cases of type Ⅳ, and 5 cases of type Ⅴ. The time from injury to operation was 2-4 days, with an average of 3 days. According to the X-ray films before and after operation, the fracture types (stable and unstable), reduction quality (according to Baumgaertner’s criteria), integrity of lateral wall and posteromedial cortex of the patients with failure of PFNA internal fixation were summarized, and the causes of failure were analyzed. Results All the 136 patients were followed up 7-18 months (mean, 13.6 months). There were 17 cases (12.5%) of PFNA internal fixation failure after operation, including 3 cases of stable fracture and 14 cases of unstable fracture; the quality of fracture reduction was excellent in 2 cases, good in 5 cases, and poor in 10 cases; 10 cases with complete lateral wall and 7 cases with defect; 9 cases with complete posteromedial cortex and 8 cases with defect. Reasons for failure of internal fixation: ① There were 8 cases of coxa varus at 12 weeks after operation due to the loss of posteromedial cortex of femoral intertrochanteric, 7 of them continued non-weight-bearing observation and fracture healed at 6 months after operation; 1 case underwent total hip arthroplasty with spiral blade excision after operation. ② There were 7 cases of internal fixation failure caused by lateral wall defect, including 2 cases of screw blade retraction, continued non-weight-bearing observation, and removed the internal fixator after fracture healing; 2 cases of malunion of rotation with the rotation of no more than 15°, fracture healed at 6 months after operation without special treatment; and 3 cases of rupture of lateral intertrochanteric wall during operation, continued non-weight-bearing observation and fracture healed at 6 months after operation. ③ The distal locking of the main screw was deviated in 2 cases during operation. One of them was found and replanted in time during operation, and 1 case was found with fracture of femoral shaft on 3 days after operation, following 1 year of non-weight-bearing observation and fracture ending healing. Conclusion The types of intertrochanteric fractures (especially unstable fractures), the integrity of the proximal lateral wall of femur, and the defect of the posteromedial cortex are the internal risk factors for the success or failure of PFNA in the treatment of geriatric intertrochanteric fractures. The effective protection of the lateral wall during operation and the good quality of fracture reduction are the external factors that must be paid attention to.