Abstract: A mathematical model has been developed to describe the behavior of solid state electrochemical reactors. The model equations are solved numerically using Newton -Raph-sons method. A simulation study based on the model has been carried out on the cogenera-tion of electrical power and useful chemicals -ethylene, ethane in the 1%Sr/La2O3 - Ag solid state electrochemical reactor. The effects of load, temperature and feed composition on the oxidative coupling of methane and output current are investigated. A comparison between the prediction of the model and the experiment results shows that the agreement can be considered as satisfactory.