Band gap of 2D triangular lattice photonic crystal with circular air holes and ring-shaped air holes in THz range was studied by using plane wave expansion method (PWM). It was found that complete band gap of circular holes was larger when the holes radius increased from 0.41a to 0.49a. For the same hole radius, ring-shaped holes photonic crystal could get the larger complete band gap than circular holes, and the optimal parameter was 0.169 8 THz when the holes radius of 0.47a, inner radius of 0.133a, was 1.15 times for circular holes structure. Transmission spectrum of ring-shaped holes photonic crystal was studied by finite-difference time-domain method (FDTD), and we designed the filter in (0.719 8 ～0.865 5) THz wave.