To study UHVDC bushings insulating properties, the establishment of a condenser bushing +/- 800kV composite finite element model with ANSOFT analysis software selection epoxy resin and high-temperature vulcanized silicone rubber composite casing was 2D capacitive field analysis, the HVDC bushing inside the exact field intensity distribution and potential distribution. The results showed that: the interior of the casing epoxy barrier forced potential distribution, so that the electric field near the flange distribution, but also makes the flange the top two bit lines and other dramatic changes, large radial potential gradient; series of electric field strength at the flange portion and the high temperature vulcanized silicone rubber sheds maximum, a maximum of 3.44MV / m, where the problem is easy to produce flashover in UHV DC operation, provide reliable reference for the design and manufacture of bushings.