The utility model relates to a preformed composite stay insulator, which belongs to the electric protection field. The preformed composite stay insulator which comprises an electric pole stay wire is characterized in that the electric pole stay wire has a segmental type structure; segmented electric pole stay wires are connected through insulators; the insulators are made of composite materials; each insulator has a group of preformed wires wound thereon; the preformed wires are tension-resistant preformed wires; and the two ends of each preformed wire are respectively connected with the electric pole stay wire. The preformed composite stay insulator which has the characteristics of simple structure, low cost, portable materials, convenient installation and simple operation enables greater performances than a conventional ceramic insulator. An installation worker is not required to be professionally trained. A common maintainer can make the preformed composite stay insulator installed. The installation efficiency is thus greatly improved. Furthermore, the preformed composite stay insulator which has the advantages of small volume, lightness and high strength can have the reliability enhanced when arranged on the stay wire.