An antenna system with a full metal back cover is provided in the present disclosure. The antenna system includes a metal back cover with a main body, a first sidewall and a second sidewall opposite to each other, a circuit board with a main ground point, a first antenna module and a second antenna module electrically connected to the circuit board. A first gap is formed between the first sidewall and the main body, and a second gap is formed between the second sidewall and the main body; the metal back cover is divided into a first metal portion including the first sidewall and a second metal portion including the second sidewall. The first metal portion includes a top slit penetrating through an edge of the first sidewall, and the second metal portion includes a bottom slit penetrating through an edge of the second sidewall.