Abstract: A mathematical model for the speed control system of two-spool turbojet engine is derived from component characteristics of the engine and construction parameters of the controller. The discretization-similitude method is adopted in the digital simulation of the nonlinear control system. The computer program written gives the steady-state and dynamic characteristics of the control system at H = 0 , V= 0 and in standard atmosphere conditions. It is indicated that the performances of the control system are improved in comparison with its prototype.