A composite target is provided and is interacted with an electron to generate an X-ray, and an energy of the electron can be changed by controlling a tube voltage at least. The composite target includes a target body and an interposing layer which is connected with the target body. The interposing layer moves a highest peak of an energy spectrum of the X-ray toward a high energy direction. The interposing layer may be a single metal or a metal mixture. Not only a low energy photon of the X-ray can be filtered by the interposing layer, but also a distribution of the low energy photon of the X-ray can be increased by increasing a thickness of the interposing layer. As the tube voltage is enhanced, an amount of a high energy photon of the X-ray generated is dramatically increased. An X-ray tube containing the above composite target is also provided.