The atomic structural model of the α phase-liquid interface region in ZA27 allo ys was set up by combining molecular dynamics theory with computer programming.T he electronic structure of α phase solid solution with rare earth elements and that of crystal-liquid growth front enriched with rare earth elements in the ZA2 7 casing alloy were investigated by the recursion method.The calculated results show that rare earth elements are more stable in the phase interface region than in α phase.This explains the fact that the solid solubility of rare earth elem ents in α phase is very small,but large in the crystal-liquid growth front.The structural energy difference between the rare earth elements in the crystal-liqu id growth front and in the α phase is greater than that in Al,which support the view point that rare earth elements enriched in the crystal-liquid growth front can make α crystal-branch melt and break down,dissociate,and propagate.Calcula tions of bond order integrals (BOIs) also show that rare earth elements in the α phase-liquid growth front are not easier than Al to solidify on the surface o f α phase,so that the growth of α grains is blocked,and the alloy is refined,t hus illucidating the modification mechanism of rare earth elements from an elect ronic level for the zinc-aluminum cast alloys.