The relay contacts’ jumping or switching on/off will cause the change of inductive load and further gas discharge. The current of relay contact on-off is small, there will be no electrical arc between contacts, but there will be a spark at the relay contacts. Due to the existence of inductance in the contact circuit, there will be overvoltage on the inductance when disconnecting the contact circuit. Together with the voltage supply in the contact gap, the contact gap that just separates a little will be broken down and discharged. Limited to energy, there will only be spark discharge. The conversion of capacitance between contacts and energy in inductance makes spark discharge disappear and reappear, becoming a high frequency signal, which will be crosstalk to related circuits by means of high frequency radiation, wire transmission and distributed capacitance, forming interference signals. Furthermore, spark discharges can also damage relay contacts and shorten the service life of contacts, so that sparks may ablate contact surfaces and make the surface uneven, resulting in failure of relay poor contact.