Abstract: The electromagnetic pulse(EMP) damage mechanism and failure modes are obtained for the input port and output port of solid state relays by current injection method. The results show that the output port would misoperate when the EMP signal is injected at input port, and the input port may lose its control function when the base-emitter junction of the transistor in input circuit is burned out by the signal, that is, the output port would not be switched into conduction when control sygnals are applied to the input. The output port can be shorted when the drain and source are damaged by injected EMP signals at output port.