Transmission component of terahertz wave in two-dimensional square lattice photonic crystal are studied with the plane-wave expansion method.The square crystal lattice of column and ellipse band gap in two-dimensional photonic crystal are calculated.We design the filter in(0.485~0.503)THz wave,and transmission component of terahertz wave in two-dimensional square lattice photonic crystal of ellipse are studied when the column change a little.This research provides a theoretic basics for the development of terahertz wave devices.