Lowering the operating temperature of the solid oxide fuel cell is important to prevent material degradation but causes a high polarization problem that slows down the electrode kinetics. The infiltration of multi-cation oxide nanoparticle catalysts on the cathode backbone can provide low activation energies to catalyze several electrochemical processes. In this study, Sm_0.5Sr_0.5CoO_3-δ(SSC55) nanoparticles were infiltrated on the surface of the La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF6428) backbone pasted on the GDC electrolyte. Electrochemical impedance (EI) spectra of the cells before and after infiltration were measured under the various thermodynamic conditions (700~600℃, pO₂=0.21~0.02atm). The parameters (Rs,Rp,Cchem, and CHN0) of the transmission line model (TLM) expressing the polarization of the cathode were analyzed in detail. Rs is the diffusion resistance of the bulk or surface and Rp is the resistance of surface reactions such as the decomposition resistance of gas molecules. Cchem is the chemical capacitance resulting from the nonstoichiometry of the electrode material, and CHN0 is the capacitance effect of the surface which varies with frequency. Trends of parameters according to the thermodynamic variables (temperature, pO₂ and current density) were sufficiently discussed by analyzing the cells before and after infiltration, and how the impedance analysis should be performed to microstructure-modified electrodes was discussed.