Abstract: The current studies of very fast transient overvoltage(VFTO) in GIS are mostly concentrated in microcosmic aspects and some achievements have been gained. Consequently, it is significant to investigate VFTO characteristics of GIS from macro respect by using existing research results in microcosmic respects. In this paper, by taking the Shahu 750 kV substation in Ningxia as an example, a dynamic arcing model is built with the software ATP-EMTP, and a detailed analysis is made of the effect of operation modes and order on VFTO and the inhibitory effect of shunt resistance on VFTO is checked. The simulation results show that the amplitude of VFTO is not only related to the operation mode but also associated with the operation order. Therefore, the VFTO does not pose a serious threat to the insulation of internal GIS and transformer windings in view of amplitude. The study results can provide a useful reference and basis for 750 kV GIS equipment development and substation operation.