The methods and the techniques set-up for evaluating the control laws for the digital Main Fuel Control Unit (MFCU) of a small thrust turbojet engine are shown. A suitable parameter defining the surge margin is considered. The paper deals with the results of a study carried out in order to evaluate the influence of engine operating parameters on the surge margin. For this aim the steady state engine simulation programs, based on the state vector technique, have proved to be very effective. Finally the codes and the obtained results have been used for calculating some suitable control laws for a digital MFCU.