The interface binding energy has been defined according to the atomic binding energy. The interface electronic structures of ZA27/CNT have been calculated by recursive method in zinc-aluminum composite reinforced by carbon nanotube. The microphysics of carbon nanotube distribution at grain boundaries of ZA27 alloy and the cause of weak interface binding in ZA27/CNT at electronic level were made clear. The research showed that the metal matrix has great effect on the density of states of carbon atoms on the nanotube, but the nanotube has little effect on the density of states of aluminum or zinc atoms in the matrix. The density of states of carbon on nanotube tends to become assimilated with matrix atoms and combine with the matrix, but as the assimilation degree is low, the interface binding strength is very weak. It is believed that similar property of atoms with matrix decorating or plated on carbon nanotube may help to reinforce the interface binding strength and improve the performance of ZA27 composite.