This work proposes three diffusion models used to simulate the reaction layer produced from silver electrode, which has been cofired with La-Si-B-O-mullite (LSBM) glass ceramic composites. In the beginning of the cofiring, the interface connection between Ag electrolyte and LSBM glass ceramic composites was full matched, and the curve of diffusion pattern fitted one of the general cases of diffusion model well. However, the interface became gradually and partially separated during the process of cofiring. As a result, the original concentration of Ag at the surface could not be maintained, and new diffusion model must be proposed. At a later stage of the experiment, the gradient of diffusion curve became smooth. The final distribution of Ag concentration didn’t reflect a general diffusion phenomenon. Total delaminated case and interfacial pitting case were considered in this research, respectively.