Comparing with periodic photonic crystal structures, quasicrystals have more interesting and complex defect modes, so that they are expected to be applied in novel defect-based photoelectronic devices. Modes of compound cavity in octagonal and dodecahedral quasicrystal investigated under the low index contrast. The results show that in the quasicrystal structure with double and several nine-air-hole-missing microcavities, it is observed not only the mode splitting, but also a new mode generation supported by a compound resonator, which covers two microcavities and the scatterers between. The field distribution of the new mode is studied. It is found that the field intensity and transmission of the new mode are much stronger than those of the modes in single defect cavity. These results will lay a theoretical foundation for the research of photonic crystal laser arrays and sensors.