On the basis of sudden change of linear absorption coefficient (LACs) in the vicinity of absorption edge, the synchrotron K-edge subtraction technique is developed to label the three-dimensional (3D) distribution of element. In this work, tomographic scans above and below the specific absorption edge of Zn are carried out and the subtracted image is used to identify and quantify the 3D distribution of Zn element inside the cell wall of Al-Zn-Mg foam. A non-uniform spatial distribution of Zn element is found in the cell wall of as-cast foam. After long solution tratment, the concentration of Zn element tended to be homogeneous. It is confirmed that the local agglomerated Zn-bearing particles exerta negative influence on the brittle cracking of the cell wall. The K-edge subtraction technique provides a powerful tool for the quantitative microstructure characterization of three-dimensional tissues.