Abstract: In order to obtain desired conventional figures of merit of when a control system is designed by qnadratie performance index, a method for selecting the elements of the weighting matrix Q by parameter optimization through repeating simulation is presented in this thesis. This method can be applied to design the speed regulator of a speed control system. Moreover, a simple and accurate method for digital simulation--Signal Flow Diagram Method as well as a program of computer aided design is introduced, and have been tested by experiments. Some results are given in the end of this thesis.