Adding creepage extender is currently recognized as an effective measure for reducing the occurrence of rain flashover of external insulation. Combining with the 800 kV UHVDC voltage divider model of an existing UHVDC converter station, the electric potentials and electric field distributions of installing creepage extender in different position respectively in clean, wet dirt condition are simulated and analyzed, simulation results show that the electric field strengths are increased near the high-voltage end of the DC voltage divider after installing creepage extender, and different installation positions have a little effect on the internal electric field distribution, which is 5% higher when creepage extender are added on its internal RC node rather than on upper or lower ends of the node.