A physical-based model has been developed and validated to unravel the complex relationships between the global solid oxide cells response and the reaction mechanisms taking place in the electrodes. This numerical tool combines three length-scales modules from the electrode microstructure up to the single repeat unit. This model allows computing the local distribution of reaction kinetic rates, current densities, and gas composition as function of the cell operating conditions. To validate the multiscale model, a special experimental setup has been developed to measure the local polarization curves along the cell length. For this purpose, a specific design of the interconnect has been proposed in order to probe the local current density on standard cells. A good agreement has been found between the experimental and simulated data for different operating conditions. The fully validated model has been used to analyze the cell operation in electrolysis and fuel cell modes. The activated reaction pathways associated with the elementary steps in the active layers have been investigated depending on the position along the cell length.