Nanoscale reactive multilayer foils can react exothermically in solid state and the reaction can self-propagate at a fixed velocity at very low temperatures. The propagating velocity is a key parameter to characterize the multilayer foils. The authors presented an extended model to predict the velocities of self-propagating reactions in multilayer foils that have alternating layers with different layer thicknesses. The reaction velocities of Al/Ti multilayer foils were calculated using the extended model and compared with experimental results. Moreover, the dependence of critical layer thicknesses on premixing thicknesses was presented.