Based on a plane wave pseudopotential method within the framework of density functional theory, equilibrium structure, bulk modulus, and relative stability were calculated for 6 kinds of TiN polytypes including B1 (NaCl structure), B2 (CsCl structure), B3 (zincblende structure), Bk (hexagonal BN structure), Bh (WC structure) and B81 (NiAs structure). Theoretical calculation also showed that TiN can not exist in B4 (wurtizite) structure. Through geometry optimization under hydrostatic pressure, the enthalpy of each TiN phase at different pressures was obtained. It was found that TiN with B1 structure is the most stable phase at pressure lower than about 345 GPa, whereas B2 TiN is the most stable at pressure above 345 GPa. Volume discontinuity and bulk modulus change can be observed during the transition from B1 to B2 phase.