Objective To study the influence of the distance of displaced fragment on the union of diaphysis fracture. Methods A wedge-shaped bone fragment was taken from central radial of the right forelimb of 120 New Zealand white rabbits for estabhshment of experimental animal model. The bone fragment was fixed to the main bone with two Kirschner wires, with certain space between bone fragment and the main bone. Then, the rabbits were divided into five groups, ie, Group A (in situ fixation),Group B (the space was 1/5 diameter of the radial shaft), Group C (the space was 2/5 diameter of the radial shaft), Group D (the space was 3/5 diameter of the radial shaft), Group E (the space was 4/5 diameter of the radial shaft). The animals were killed at 2, 4, 6, 8 weeks after operation. X-ray photos were taken to observe the fracture healing and the improved Gary X-ray used for scoring. HE staining after tissue section was employed to observe the histomorphological changes of fracture healing. Immunohistochemical method was used to determine expression of BMP-2. Results X-ray findings showed insignificant statistical difference between Group A and Group B, delayed union in Groups C and D and nonunion of bone absorption in Group E. Morphological observation showed same change in fracture site in Groups A and B lout significant late in emergence, formation and remodeling of the callus in the other groups compared with Group A, mainly with delayed fracture union or nonunion. There was no statistical difference in expression of BMP-2 between Group B and Group A (P ＞ 0. 05), but there was statistical significance in Groups C, D and E compared with Group A at 2 weeks (P ＜0.01). There was statistical difference between Group E and Group A at 4 weeks (P ＜0. 01) but no statistical difference at 6 and 8 weeks between either two groups (P ＞ 0. 05). Conclusions The distance of displaced fragment will influence fracture healing. The larger distance of the displaced fragment will beget more obvious influence on fracture healing. When the distance is more than 2/5 diameter of the bone shaft, the fracture will present union disorder.