This paper studies dispersion characteristics of the transverse magnetic(TM) mode for two-dimensional unmagnetized dielectric plasma photonic crystal by a modified plane wave method.First,the cutoff behaviour is made clear by using the Maxwell-Garnett effective medium theory,and the influences of dielectric filling factor and dielectric constant on effective plasma frequency are analysed.Moreover,the occurence of large gaps in dielectric plasma photonic crystal is demonstrated by comparing the skin depth with the lattice constant,and the influence of plasma frequency on the first three gaps is also studied.Finally,by using the particle-in-cell simulation method,a transmission curve in the Γ-X direction is obtained in dielectric plasma photonic crystal,which is in accordance with the dispersion curves calculated by the modified plane wave method,and the large gap between the transmission points of 27 GHz and 47 GHz is explained by comparing the electric field patterns in particle-in-cell simulation. This paper studies dispersion characteristics of the transverse magnetic (TM) mode for two-dimensional unmagnetized dielectric plasma photonic crystal by a modified plane wave method. First, the cutoff behavior is made clear by using the Maxwell-Garnett effective medium theory, and influenced by of dielectric filling factor and dielectric constant on effective plasma frequency are analysed. More over, the occurence of large gaps in dielectric plasma photonic crystal is demonstrated by comparing the skin depth with the lattice constant, and the influence of plasma frequency on the first three gaps is also studied. Finished, by using the particle-in-cell simulation method, a transmission curve in the Γ-X direction is obtained in dielectric plasma photonic crystal, which is in accordance with the dispersion curves calculated by the modified plane wave method, and the large gap between the transmission points of 27 GHz and 47 GHz is explained by comparing the electric field patterns in particle-in-ce ll simulation.