Abstract: The paper used Simulink toolbox of Matlab to establish simulation model of single phase grounding fault of underground NUS.It expounded principles of zero sequence power line selection algorithm and zero sequence power line selection algorithm with compensation,introduced simulation structure of line selection model based on zero sequence power line selection algorithm,and adopted method of simulating operation mechanism of line selection device to simulate and analyze the both line selection algorithms.The simulation results showed that the zero sequence power line selection algorithm has high veracity of line selection,strong anti-interference ability and quick response speed to faults and suits to be line selection algorithm of single phase grounding fault of underground NUS.