Abstract: An engineering method of optimal discrete regulator design for digital flight control system is described. There are various existing methods available for calculating the transition matrix （T） and its integral. However, methods for calculating weighting matrix numerically in the presence of coupling between the state and control variables are not found. This paper presents an engineering method, with it, the continuous quadratic performance criterion can be simply transformed to a discrete version. The C* and D* criterion and some additional flying quality requirements are used for constituting the quadratic cost function and to precisely determine the value of elements of weighting matrix without repeated adjustment. An example using this method to synthesize the stability augmentation system and autopilot is given. Design results are satisfactory, and it shows that, for the longitudinal system, at slow sample rate, less than 10 samples per second, optimal control laws are still adequate to ensure a good system response; for the lateral-directional system, however, the system response is more sensitive to the change of sample rate, and system performance shall be degraded with sample rate slower than 10 samples per second. Under the condition of same performance criterion, the optimal control gains always increase with the sample rate.