The invention discloses a method for determining an impedance parameter of a giant hydro-generator set based on neutral point grounding and relates to a method for determining parameters of a ground-side power generating device of a giant hydro-generator set. The method comprises: parameter configuration zones of a resistor R and a reactor XL are determined; according to the determined parameter configuration zones of the resistor R and the reactor XL, a relationship curve between the resistor R and the reactor XL is drawn; and according to an under-compensation zone of the inductance, a numerical point enabling a transient over voltage Up to be 2.6pu is searched at corresponding curves of the resistor and the reactor within a zone range of [XS0,+infinit], and the determined RS and XS arecorresponding configuration parameters. On the basis of combination of the technical economy and technical feasibility, a combined cabinet type impedance generator neutral point grounding device is installed according to final grounding parameters of the resistor R and the reactor XL. Therefore, equipment in a single equipment cabinet can be modified or replaced; and modification becomes easy andflexible.