We study the steady and transient optical properties of electromagnetically induced transparency(EIT), spontaneous emission, and the photonic switching for a four-level atomic system embedded in photonic band gap(PBG) structures. The theoretical analysis shows that a special density of modes (DOM) can induce abnormal spectrum of absorption, dispersion，spontaneous emission and transient gain without inversion, and they can be controlled by an externally applied coherent light. Furthermore, we discuss the effects of the nonsingular DOM on the EIT windows and on the photon switch in detail.