Abstract: The affecting factors of short-circuit currents of 1 000 kV and 500 kV bus-bar at UHV AC substation are analyzed based on the components of corresponding self-impedance. And then the proportions of all factors to the short-circuit currents at 1 000 kV bus-bar and 500 kV bus-bar are proposed and determined, including the configuration of 1 000 kV power grid, the main transformer and the configuration of 500 kV power grid. The results indicate that the short-circuit currents of 1 000 kV bus-bar are greatly affected by the configuration of 1 000 kV power grid. The 500 kV power grid and the main transformer have a dominant influence on the short-circuit currents of 500 kV bus-bar at UHV AC substation. The results can provide theoretical support and decision-making reference for the optimization of short-circuit limit.