A method is introduced to tune and optimize the photonic band gaps （PBGs） of two-dimensional photonic crystals （PCs）. PBGs between the bands at low frequency can be tuned by an additional atom rod at arbitrary positions. Moreover, fixing up the two atom rods at optimal positions and tuning the lengths of the two cylinders, the normalized gap widths of PBGs could be enlarged with a suitable configuration. The results also show that the setting up of large PBGs depends on different degrees of symmetry of the system in the case of two atom rods in a unit cell, the larger PBGs at higher frequency require lower symmetry.