An improved composite cup structure, which comprising: an inner plastic cup and an outer paper cup; of which the composite cup is manufactured from paper and plastics by a ratio of 7:3; the rims of both inner plastic cup and outer paper cup are provided with outwards curled edges, in particular, the curled edge of the inner plastic cup is slightly larger than that of the outer paper cup, and a flat surface is formed on the top; besides, an extension sheet of any shape is formed on the curled edge towards the cup bottom; when the inner and outer cups are overlapped, the curled edge of the inner plastic cup could cover the curled edge of the outer paper cup, thus forming a heat-insulating, leak-proofing composite cup of excellent strength; the extension sheet contributes to the separation of inner and outer cups for classification and recycling.