Multi-antenna system

A multi-antenna system including a substrate, a ground element, a first antenna element, a second antenna element and a decoupling element is provided. The ground element is disposed on a first surface of the substrate, and the decoupling element is disposed on a second surface of the substrate. Ground portions of the two antenna elements and a first connection terminal of the decoupling element are electrically connected to the ground element. The decoupling element is spaced a first decoupling distance from a part of the first ground portion, and the decoupling element is spaced a second decoupling distance from a part of the second ground portion. A phase difference relative to the two antenna elements is generated by the decoupling element, the first decoupling distance and the second decoupling distance so as to eliminate interference energy between the two antenna elements.