In order to gain the propagation characteristics of two-dimensional triangular lattice photonic crystal in THz range,the band gap structure and density of photon states were calculated by plane wave expansion method(PWM). It was found that the maximum photonic band gap was observed when f =0.9069 in E polarization and f = 0.7364 in H polarization,and the maximum absolute photonic band gap was gained when f=0.8358.It was found that large photonic band gap can be obtained by increasing D-value of dielectric constant. The photonic band structure was also shown by the photonic density of states. This result provides theoretic basis for the development of THz devices.