Thermally sprayed ceramic coatings such as plasma-sprayed alumina exhibit a composite microstructure actually due to the presence of defects such as pores, inter-lamellar and intra-lamellar cracks. These second phase-typed features influence the mechanical behaviour of the coating dramatically. In this study, a microstructure simulation of plasma-sprayed alumina was developed for the optimizing of component properties such as electrical tool used in the oil industry. This approach consisted of a finite-element analysis of mechanical properties from simulated microstructures. Several composite microstructures were tested from air plasma spraying of alumina. Various degrees of porosity and cracks could be obtained from different spraying conditions. Every composite microstructure was studied using a quantitative image analysis of scanning electron microscope (SEM) cross-sections. A finite-element model based on the actual microstructure was developed. First, two-dimensional (2D) finite elements meshes were created from SEM images of microstructures. Then, in order to have a realistic representation of the three-dimensional (3D) microstructure, pictures were obtained using X-ray microtomography. Volume tetrahedral grids were generated to simulate the properties of alumina coatings. This work studies the contribution of every part of the alumina coating to the final properties and shows potentials and limitations of the 2D and 3D computational approach.