Compared with the traditional finite-difference time-domain method, the symplectic finite-difference time-domain method has high precision and low dispersion. The traditional finite-difference time-domain method arises low accuracy and great dispersion error. Also it has destroyed the symplectic structure of the Maxwell’s equations and causes the poor stability. But, the symplectic finite-difference time-domain method can overcome these shortcomings and ensure the accuracy and stability of the whole simulation. So, this paper researches the band-gap characteristics and the transmission coefficient of the plasma photonic crystals with the symplectic finite-difference time-domain method and traditional finite-difference time-domain method. The results have proved the advantages and feasibility of the symplectic finite-difference time-domain method.