For the first time, the impacts of solid oxide fuel cell (SOFC) cathode/contact paste interface roughness on mechanical strength are quantified using a particle based numerical technique in micro-scale. This work identifies a potential new direction to develop high strength SOFC stack structures to enhance SOFC longterm durability with most commonly used material. To model the effect of different interface roughness values on the integrity of the dissimilar material joint as well as the fracture behavior of the bonded interface, a discrete element model (DEM) method is adapted due to many unique advantages. The model demonstrates that interfacial toughness increases with interfacial roughness and sintering temperatures. In particular, the roughened interface can increase ultimate mechanical strength to a factor of 2-3 compared with the smooth interface. Moreover, contact paste with higher stiffness properties can be beneficial in terms of delaying the onset of the initial interfacial damage at rough interfaces. The results also show that toughness decreases with increasing strength ratio between the interface and contact paste. It is expected that this study can provide guidance to improve SOFC cathode design with better mechanical strengths, which would benefit the mechanical integrity of the SOFC stack. (C) 2020 Published by Elsevier Ltd.