In the present study, the electrochemical performances of different LSCF-GDC microstructures are numerically calculated in order to investigate the effects of GDC particles and GDC pillars on LSCF cathode microstructures with various particle sizes. Lattice Boltzmann method (LBM) is applied for solving the governing equations. It is found from the numerical results of pure GDC and LSCF-GDC composite cathodes with various particle sizes that GDC addition improves LSCF cathode electrochemical performance. This performance improvement is more pronounced for cathodes with smaller particle sizes and when operated at lower temperatures. In addition, it is shown that LSCF cathode with GDC pillars can enhance the performance of the cathode. The GDC pillars are even more effective when the reactive region of the cathode becomes thin by using small size powders.