The coupling properties of defect modes between the double-defect microcavities in the octagonal quasi-photonic-crystals are investigated under a low-refractive-index contrast based on the organic semiconductor luminescent materials. The study results show that, in the quasicrystal structure with double nine-air-hole-missing microcavities, it is observed that not only the modes split, but also a new mode in the composite cavity constructed by the double-defect microcavities and the intermediate scatterers. Based on this, by using the three-dimensional field distribution and the phase relationship among the defect modes, the physical mechanism of mode-coupling is disclosed. These results provides a theoretical foundation for the future design and fabrication of organic semiconductor photonic crystal devices in visible light band.