Gas-insulated transmission line（GIL）has the advantages of compact structure

safety and reliability

large transmission capacity

small capacitance current and no electromagnetic interference. The insulator supportsthe conductor in GIL

its performance determines the technical level and the long-term reliability of GIL. This paperanalyzes the factors of insulation performance for epoxy resin composite insulator

including the root R of column insu-lator

the angle of column insulator

the diameter of low voltage terminal component

the epoxy thickness of highvoltage terminal component. The results are as follows: under the permission of the structure

the larger of the root R of column insulator

the smaller the electric field intensity;the larger the angle of column insulator

the smaller theelectric field intensity

however

the greater the electric field intensity on the low voltage terminal component

themore consideration should be taken in the design. The larger of the low voltage terminal component diameter

thesmaller the intensity of the electric field;the larger of the epoxy thickness of high voltage terminal component

thelarger the value of the surface vector of the insulator is

the smaller the electric field intensity of the high voltage ter-minal component is

the design should be considered at the same time. The UHV GIL column insulator which devel-oped with above theories has passed the insulation type test

which indicates the reliability of the related conclusions.