The reduction of complex linear system is always a very important topic in many courses. In Signal and System it is the analysis of Signal Flow graph(Mason's Rule). In Signal Processing it is to find out the system function from complex filter structure. In Automatic Control it is the reduction of structure diagram of complex systems. The theory and calculation are always very difficult and tedious. In this paper, A general model for these linear systems using matrices is deduced. Then with the aid of MATLAB, this problem can be solved quickly and precisely. It is much superior to all previous methods.