Photonic crystal is a structure with periodic dielectric constant and it has photonic band gap, in which the electromagnetic wave can not propagate in the structure. Two-dimensional slab photonic crystals can be fabricated by etching periodic air holes on a slab substrate, which has been investigated and applied extensively because of their good control of light propagation. Photonic crystal micro-cavities and waveguides can be achieved by introducing defects in the two-dimensional slab photonic crystal. The coupling of micro-cavities and waveguides can be controlled by adjusting geometric parameters, so as to realize the optical devices based on two-dimensional slab photonic crystals such as optical switching, optical storage and single photon source, etc. Properties of the micro-cavities and waveguides of two-dimensional slab photonic crystals are introduced, and their coupling control and potential applications in optical quantum information processing are discussed as well.