The primary interface between titanium alloy bone implants and bone is mainly composed of a titanium dioxide/hydroxyapatite interface. However, anatase phase titanium dioxide/hydroxyapatite interfaces have been less extensively studied. This paper employs density functional theory (DFT) to investigate the anatase/hydroxyapatite (HA) interface. Bonding behavior between the interface atoms is characterized using bond length, density of states (DOS), and electron density metrics. Based on this foundation, this paper proposes two types of cation-centered bonding networks: (1) a bonding network centered on Ca ions, and (2) a bonding network centered on Ti and P ions. Using the charge variations before and after the formation of surfaces and interfaces, this study characterizes the active and inert bonding sites. Calcium (Ca) is identified as the most valuable cationic active site at the interface. At the interface, the active sites in one phase precisely form bonds with the inactive sites in the other phase. Utilizing these insights, researchers and engineers can develop bone implants with improved mechanical properties and biocompatibility, leading to better patient outcomes in orthopedic and dental surgeries.