Abstract: The dynamic fracture properties of the Al-Zn alloys including ZA8,ZA27 and ZA35 alloy changing with the chemical composition were studied by using Hopkinson bar apparatus at different loading rates.The fracture morphology of the sample was observed by means of SEM.The results show that the content of α phases (FCC) in the alloy increased with the increase of Al content of the alloy at a constant loading rate.The fracture morphology was changed from cleavage to dimple,and the dynamic fracture energy and the loading rate sensitivity increased gradually.With the increase of loading rate,only the fracture morphology of the ZA8 alloy did not change.The fracture morphology of the ZA27 and ZA35 alloy changed from dimple to quasi-cleavage,which made the dynamic fracture energy decreased with the increase of loading rate,and the loading rate sensitivity of the two alloys decreased gradually.