The nucleation and growth characteristics of pre eutectic solid solution phase in Zn Al alloys with aluminum content of w （Al）=3.0%～28.4% were studied with quantitative metallographic analysis of probes prepared by liquid quenching during the unidirectional solidification process. The results showed that both pre eutectic Zn rich phase and Al rich phase have the same features of instantaneous nucleation but have different characteristic growth. The pre eutectic Zn rich phase grows more rapidly after nucleation

and then more slowly while pre eutectic Al rich β and α phases do more slowly after nucleation and more rapidly with enough under cooling. The β phase not only grows on α phase by peritectic reaction of L+α→β

but also nucleates directly from the remainder liquid phase.