Electronic and atomic structures of interfaces between TiN coatings and Al2O3–WC composites were investigated by Density functional theory (DFT) calculations. As typical examples, interfacial orientation relationships of TiN(001)/Al2O3(0001), TiN(001)/WC(0001), TiN(111)/Al2O3(0001), and TiN(111)/WC(0001) were chosen. It was found that the TiN(111)/Al2O3(0001) and TiN(111)/WC(0001) interfaces have interfacial structural units of six‐fold coordinated triangular prisms centered on Ti atoms. In contrast, those of the interfaces with TiN(001) tend to have more distorted structure units due to their larger lattice misfits. Theoretical works of separation showed that interfacial strength is much more increased at the TiN(111) interfaces, as compared to those at the TiN(001) interfaces. Accordingly, experimental controls of TiN‐coating orientations on Al2O3–WC composites were attempted by using the cathodic arc ion plating method. It was found that orientations of (111) in the TiN coatings can be more enhanced and then interfacial mechanical strengths and hardnesses of the TiN coatings can increase more with rising bias voltages.