Abstract: The cast Al-Si alloys are especially suitable for the production of large thin-walled complex structural castings.Improving the fluidity and heat crack resistance of the alloy is of great significance to improve the qualified rate of castings.After combing, comparing and analyzing the fluidity and thermal crack sensitivity of cast Al-Si alloy, it is concluded that the type and content of elements have great influence on the fluidity of the alloy. The alloy fluidity is closely related to the temperature of dendrite coherence point, and the difference can be reflected by measuring dendritic coherence point. It is more appropriate to study the fluidity of the alloy by using the difference between pouring temperature and dendrite coherence point temperature. Combined with the solidification temperature range of the alloy and the grain morphology at the front end of the fluidity sample, the way of flow stopping of the alloy can be judged more accurately. Alloy elements have great influence on the thermal cracking sensitivity of the alloy. At present, the mechanism of thermal crack formation is mainly solidification shrinkage compensation theory, strain theory and brittle shrinkage theory.