A bone fusion device includes a main body (1) and a movable frame (2). The main body (1) has an accommodation hole (15) penetrating a top surface (13) and a bottom surface (14) thereof. The top surface (13) and the bottom surface (14) are provided with a plurality of first teeth (181, 182). The movable frame (2) is located in the accommodation hole (15). The movable frame (2) has a through hole (25) longitudinally penetrating a first surface (23) and a second surface (24) thereof. A first end (21) of the movable frame (2) is fixed to the front end (11) of the main body (1), and a second end (22) is suspended relative to the rear end (12) of the main body (1). The first surface (23) and the second surface (24) are provided with a plurality of second teeth (281, 282). The movable frame (2) is transversely formed with a groove (29) to define an upper portion (20A) and a lower portion (20B), enabling the upper portion (20A) and the lower portion (20B) to be elastically expanded with the first end (21) as a fulcrum. When the main body (1) is implanted between two bones (S1, S2), the first teeth (181, 182) provide a first acting force, the second teeth (281, 282) provide a second acting force, and the second acting force is not equal to the first acting force. Accordingly, the second acting force of the second teeth (281, 282) to act on the two bones (S1, S2) and the first acting force of the first teeth (181, 182) to act on the two bones (S1, S2) are differential and complementary to strengthen the stability of engagement and to slightly stimulate the two bones for expediting fusion of the two bones (S1, S2).
