Based on the equivalent circuit of a resonant grounded system， the changes of the transient characteristics are analyzed theoretically when the fault resistance changes. The study indicates that the circuit is under-damped firstly， then it enters the damping state， and finally makes the transition to under-damped state. A resonant circuit model with cables is established， and the changing law of the zero-sequence transient current spectrum is analyzed when the cables are added to the distribution network and when the fault angle， fault resistance and fault distance are changed. Simulation results show that the adding of cables makes the spectrum of zero-sequence transient current move to a lower-band. Fault resistance has great influence on the spectrum of zero-sequence transient current.