Over the past decade the Anaerobic Digestion Model No1 (ADM1) proved to be a powerful tool for predicting and control of anaerobic digestion process, while the approach of characterizing sewage sludge into carbohydrates, lipids and proteins requires measurements that are not routinely available on sewage sludge and so The ADM1 model has been regarded as too complex for practical applications. The main purpose of this research was to assess the steady state model against the ADM1 in order to determine the possibility of using it for anaerobic digestion of different types of sewage sludge such as primary sludge, mixture of primary sludge and waste activated sludge, and mixture of primary sludge and trickling filter sludge. The steady state model was able to predict the effluent COD concentration, Biogas production and pH value of all types of tested sludge used in this research paper and the results showed a lack of significant difference between the steady state model predictions and the ADM1 predictions. Therefore, the steady state model proposed by Sotemann preferred to be used for the simulation and modeling of the anaerobic digestion of any type of sewage sludge –in case of steady state operation- because of its ease and its applicability.