Abstract: Modern power systems are constantly evolving, and distance protection enables selective removal of faulty components.Taking the directional impedance relay as an example, according to the distance protection for transmission lines, MATLAB is used to model and simulate the analysis.0° wiring method is used to illustrate the change rule and reasons of various phases due to different transition resistance under different short-circuit fault types, and the effectiveness of Simulink to analyze the distance protection process of transmission lines is verified.According to the phase position of directional impedance relays under different short-circuit fault types, the advantages and disadvantages of directional impedance relays are analyzed, which provide reference for the analysis of distance protection.