Computer simulation plays an instrumental role in modern tool material design. In this study, we have calculated the temperature and pressure conditions for the phase transition of Si3N4 from α to β using first principles. The simulation results show that the phase transition temperature is 1330 K at a phase transition pressure of 32 MPa. The modulus of elasticity, hardness, ductile/brittle properties (B/G), Poisson's ratio, elastic anisotropy, and phonon spectral curves at the phase transition point were also calculated for the material at temperatures ranging from 873 K to 2073 K. According to the phase transition conditions, the surface energies of β-Si3N4 and TiC interfaces were calculated, and 4-layer models of Si3N4/TiC interfaces were constructed. The total energy and adhesion work of the Si3N4(110)/TiC(100) interface were analyzed by molecular dynamics. The results show that the Si3N4(110)/TiC(100) interface exhibits the maximum total energy and adhesion work of 12,806.62 eV and 2.33 J/m2, respectively, indicating that the interface bond was the most stable. Furthermore, the mechanical properties of different interface models were calculated and compared. The effects of Si3N4(110)/TiC(100) interfacial 5-layer and 6-layer crystalline surfaces and Si and Ti vacancy defects on the mechanical properties of the interfacial model were further investigated. The Si3N4/TiC composite ceramic tool material was prepared experimentally based on the results of simulation, and the properties show reasonable agreement.