The complex spatial electromagnetic disturbance of GIS substation will be coupled and invades the sink node equipment of the wireless sensor network of intelligent substation, resulting in packet loss, bit error and abnormal operation. In serious cases, it will cause permanent damage to the equipment and the collapse of the entire wireless network system. Several smart substations with different networking types are investigated in this paper, and the induced currents of communication lines and power lines of sink node equipment in a 110 kV smart substation are measured under steady-state conditions; The coupling mechanism between space electromagnetic field and sink cables is analyzed; The near-field and far-field coupling model of the communication line and power line of the sink node is established, and the induced voltage of the core wire is calculated; The noise tolerance of the internal circuit devices is proposed to judge the interference degree of the core induced voltage to the sink node. In this paper, the reliability of the sink node in the complex electromagnetic environment is analyzed and suggestions are put forward to provide technical support for promoting the large-scale construction of the power Internet of Things.