Photonic crystal not only can be used to inhibit the spontaneous emission and redistribute the energy into useful forms, but also can be designed to control and confine photons. Since the concept was introduced by John and Yablonovitch in 1987, there have been discussed the machinery of broadening the band bap and a quest for the optimal structure. Band structures of two-dimensional photonic crystals with different lattices and scatters of air hole of various shapes, orientations and sizes are investigated by the plane wave expansion method. The calculation results suggest that the variation of the photonic crystal band bap is attributed to the competition between symmetry and quantum confinement effects.