A pre-fabricated dome and a spherical structure include strut assembly sets, into which glass panels or synthetic resin transparent plates are to be inserted, are assembled into 5 sets of hexagonal modular assemblies around a pentagonal assembly to build a primary pentagonal modular assembly, and further 5 sets of primary pentagonal modular assemblies, into which upper and lower, (outer and inner) struts are assembled in 2 layers (of outer and inner walls), are interconnected to build a semi-spherical dome, and if 12 sets of primary pentagonal modular assemblies are assembled, a solid cylindrical structure can be built to provide a perfect block between the outdoor and the indoor so that the room temperature will not be affected at all by the outdoor temperature.