Accurate analysis of the electromagnetic interference characteristics in the secondary equipment circuit in an UHVDC converter station is the premise and basis for formulating the protection measures. The broadband equivalent models of the main elements of a ±800kV UHVDC converter station, such as the converter valve, converter transformer and smoothing reactor are built in this paper, and the conducted voltage characteristics of the primary circuit are obtained accordingly. Combined with the broadband equivalent model of Capacitor Voltage Transformer and secondary circuit cables, the conducted voltage characteristics in the secondary equipment circuit under different operation modes are researched, the influence of the cable length and burden rate are studied.