We Dropose a new method to form a novel controllable photonic crystal with cold atoms and study the photonic band gap(PBG)of an infinite 1D CO2-laser optical lattice of 85Rb atoms under the condition of quantum coherence.A significant gap generated near the resonant frequency of the atom is founded and its dependence on physical parameters is also discussed.Using the eigenquation of defect mode,we calculate the defect mode when a defect is introduced into such a lattice.Our study shows that the proposed new method can be used to optically probe optical lattice in situ and to design some novel and controllable photonic crystals.