A mobile device, comprising: an antenna structure, comprising a radiation element, a feeding element, a grounding branch, and a signal source; characterized in that the mobile device further comprises: a tunable circuit element (152, 252, 730, 815, 835, 855, 875), coupled to the radiation element, wherein the antenna structure and the tunable circuit element are disposed in a clearance region (750, 950) of an inner space of the mobile device, the inner space of the mobile device being divided into the clearance region (750, 950) and a circuit board region (760, 960) and the clearance region being a non-metal region to avoid interference with radiation performance of the antenna structure; and the grounding branch disposed in the clearance region comprising one or more electronic components disposed on the grounding branch of the antenna structure and being electrically connected to the antenna structure to avoid interference with radiation performance of the antenna structure; a tuner, having a variable impedance value, and coupled between the tunable circuit element and the signal source, wherein the tuner and the signal source are disposed in the circuit board region (760, 960) of the mobile device, wherein the circuit board region is divided from the clearance region; a ground plane, disposed in the circuit board region of the mobile device; the grounding branch, disposed in the clearance region, coupled to the ground plane, and forming the radiation element, wherein a slot is formed between the ground plane and the grounding branch; and the feeding element, extending across the slot, wherein the signal source is coupled through the tuner, the tunable circuit element, and the feeding element to the grounding branch. an antenna structure, comprising a radiation element, a feeding element, a grounding branch, and a signal source; a tunable circuit element (152, 252, 730, 815, 835, 855, 875), coupled to the radiation element, wherein the antenna structure and the tunable circuit element are disposed in a clearance region (750, 950) of an inner space of the mobile device, the inner space of the mobile device being divided into the clearance region (750, 950) and a circuit board region (760, 960) and the clearance region being a non-metal region to avoid interference with radiation performance of the antenna structure; and the grounding branch disposed in the clearance region comprising one or more electronic components disposed on the grounding branch of the antenna structure and being electrically connected to the antenna structure to avoid interference with radiation performance of the antenna structure; a tuner, having a variable impedance value, and coupled between the tunable circuit element and the signal source, wherein the tuner and the signal source are disposed in the circuit board region (760, 960) of the mobile device, wherein the circuit board region is divided from the clearance region; a ground plane, disposed in the circuit board region of the mobile device; the grounding branch, disposed in the clearance region, coupled to the ground plane, and forming the radiation element, wherein a slot is formed between the ground plane and the grounding branch; and the feeding element, extending across the slot, wherein the signal source is coupled through the tuner, the tunable circuit element, and the feeding element to the grounding branch.