The defect modes in two-dimensional square dielectric photonic crystals have been calculated, and the coupling characteristics of the defect modes of point defects have been simulated systematicly when the numbers of defects, the distance between two defects and the direction of coupling vary respectively, which is based on the results of the calculation performed by solving Maxwell's equations using the supercell plane-waves expansion method. The results show that, split photon states change according to the distance between localized photons. When the defect separation becomes large, the interaction between localized modes becomes small, and the parity of the defect mode alternates as the inter-defect distance varies. The defect modes form a defect band in a photonic band gap when the number of coupled point defects increases. The parallel propagating plane waves can excite both the even and odd defect modes. However, the perpendicularly propagating plane waves can excite only the even mode. The defect modes of point defects can be decoupled along diagonal directions where the defect mode decays rapidly, each single micro-cavity is not coupled to its neighbor, and the eigenfrequency is independent of the wavevector.