Safety, lifetime and rated current of active parts in a high voltage SF6 gas insulated switchgear (GIS) are partly determined by the material properties and forms of support insulators which are made of solid insulation materials. Recently these epoxy support insulators are mostly casted from the mixture of two- or three components epoxy resins. In this work the calculation of the electric field on high voltage 245 kV single-phase metal-enclosed support insulators which manufactured by CG Electric Systems Hungary Zrt. is presented with two finite element softwares (Gmsh and GetDP, ANSYS) in different arrangements where the comparison of the solutions are also taken into account. Then the different stresses of the support insulators are discussed with the rated insulation levels on the base of the standards and the analysis of several patent descriptions relating to proposed solutions with its advantages and disadvantages. Finally some new support insulator forms are developed with an iteration procedure which are suitable for manufacturing a prototype.