The visualization of the detailed microstructure of plasma sprayed ceramic coatings is carried out through quantitative analysis of the distribution of the infiltrated element as a tracer. A method to characterize quantitatively the microstructure of spray coating is proposed based on an idealized layer structure model and the distribution of the tracer in the coating. The microstructural parameters include mean thickness of lamellae, bonding ratio between flattened lamellae, distribution and average lamellar interface gap, and vertical crack related parameters. The experiment is performed for plasma sprayed alumina coating with the infiltration of Cr2O3 through chromium acid. The Cr distribution along the lines perpendicular to lamellae is obtained by EDAX line analysis in the form of digital signal at intervals of 2 µm. The processing method of the signal to evolve the structural parameters is introduced.