Al-Zn-Mg-Cu high strength alloy ingots were produced by DC（direct-chill casting）.The distribution of porosity in the cross section of the DC ingot was investigated by the precision density method（Archimeds’ principle）.The change of porosity rate in the cross section as well as in the thickness and width direction of the alloy was presented.The results show that:at the cross section of the ingot

porosity rate is increased gradually from the surface to the center of the ingot

and at thickness direction

porosity rate in the zone of 1/2width and 1/4width exhibits an overall escalating trend from the surface to the center of the ingot.Meanwhile

at width direction

from the surface to the center of the ingot

porosity rate in the zone of 1/2thickness is firstly rapidly increased and then fluctuated in a certain range

while in the zone of 1/4thickness

porosity rate is firstly increased slightly and then decreased gradually.Porosity rate is closely related with the cooling rate in the ingot.With increasing in cooling rate

the porosity rate is decreased

while porosity rate is increased near center of the ingot as a result of low cooling rate.