Background Few studies focus on the treatment of femoral head fracture combined with posterior hip dislocation, and the safe interval time between injury and hip reduction remains controversial. The purpose of this study was to evaluate and compare the outcome of early and delayed hip reduction in the surgical treatment of femoral head fracture combined with posterior hip dislocation. Methods A total of 71 patients were evaluated in this retrospective study. Based on the time to hip reduction, they were divided into early group (within 6 h after injury) and delayed group (between 6 and 12 h after injury). The two groups were compared in reference to hospital day, fracture healing time, the occurrence of complications and final functional outcome. The Thompson-Epstein criteria, modified Merle D'Aubigne and Postel scores, visual analog scale (VAS) and Medical Outcomes Short Form 12-item questionnaire score (SF-12) were used for final functional evaluation. Results The mean hospital stay and fracture healing time in the early group were significantly lower than those in the delayed group. The incidence of infection, post-traumatic osteoarthritis, and avascular necrosis of the femoral head (ANFH) in the delayed group were higher than that in the early group. The early group had better functional outcomes in terms of Thompson-Epstein criteria, modified Merle D'Aubigne and Postel scores and physical component scale (PCS) than the delayed group. Conclusions For the treatment of femoral head fracture combined with posterior hip dislocation, the early and prompt hip reduction can effectively facilitate the fracture healing and patient rehabilitation, and obtain a better functional outcome.