The invention discloses a high electromagnetic transmission composite structure for reducing the transmission loss of an electromagnetic wave. The high electromagnetic transmission composite structure includes a first composite structure layer, a second composite structure layer, and a first buffer layer. The first composite structure layer has a first thickness and a first dielectric constant. The second composite structure layer has a second thickness and a second dielectric constant. The first buffer is disposed between the first composite structure layer and the second composite structure layer and has a third thickness and a third dielectric constant. The transmission loss of the electromagnetism wave can be adjusted by adjusting the first thickness, the first dielectric constant, the second thickness, the second dielectric constant, the third thickness, and the third dielectric constant.