Abstract: With directional solidification-liquid quenching and definite quantity analysis of metallographic, this paper studied the micro-solidification characteristic of ZA28.4 alloy. The research is shown that pre-eutectic aluminum-rich phase of high aluminum ZA alloys form core secondarily. With the increasment of cooling rate,the grain density of pre eutectic aluminum-rich phase increases firstly and decreases secondly, the grain density of firstly forming phase and casting state increase gradually.