This paper presents a new modeling method based on signal flow graph correlation matrix. Firstly, according to the signal flow graph, a signal tree can be selected. Based on the signal tree, a signal branch and the node can be added, finding independent loop - loop incidence matrix. The correlation matrix can determine the relevance of the loop, and help seek its loop gain. Moreover, mathematical model can be figured out by using Mason formula. Theoretical analysis and experimental results show that when the nodes increase, this method is simpler and the meaning of the formula is clearer. In comparison to existing methods, our method has obvious advantages in calculation and expression. Our method makes the model of the system more accurate, and the modeling process becomes faster and more convenient.