A frustum photonic crystal which is working in the terahertz band is designed.The CST MWS is used to study the band-gap properties of photonic crystals.From the simulation in THz range from 0.3 THz to 1THz，the frustum photonic crystals have photonic band gap.Compared with the general cylindrical photonic crystals，the photonic crystals are simulated by relevant simulation software，it is found that band gap range moves with the change of the parameters，which changes radius of frustum top from 0.05 to 0.1 mm spacing with 0.01 mm，it is found that band gap shifts to high frequency with the decrease of the radius at the top of the frustum.Changing the lattice constant from 0.2 to 0.3 mm spacing with 0.05 mm，it is found that the band gap shifts towards low frequency with the increase of lattice constant.The research results provide theoretical basis for the study of the terahertz photonic crystal waveguide.