The electro-thermal effect is accompanied by the electrothermal effect when the safety spark test electrode breaks the inductance circuit, which plays a key role in electron emission, making the cathode a source of thermal field emission. In-depth analysis of the microscopic morphology of the surface of the test electrode, so as to establish a physical model of the micro-protrusions on the surface of the test electrode of the cadmium disc. Deduced the mathematical expression of the electron emission current density under the action of heat conduction-field, and numerically calculated the relationship between the thermal field-induced current density and temperature of different electrode materials, and found that the tungsten wire and cadmium disk electrode electrons emit electrons during the arc-building phase of the inductance circuit The mechanism is different. Based on this, numerical simulation of the effect of different applied electric fields on the temperature of micro-protrusions on the surface of the cadmium disk electrode has laid a theoretical foundation for further research on the mechanism of inductive breaking and arcing.