An antenna system and a terminal device, where the antenna system includes a first feed point, a first ground point, a second feed point, a second ground point, a third ground point, a fourth ground point, a first radiator, a second radiator, a first resonance structure, and a second resonance structure, where the first feed point is coupled to the first radiator, the second feed point is coupled to the second radiator, the first radiator is coupled to the first ground point, and the second radiator is coupled to the second ground point, the first resonance structure is electromagnetically coupled to the first radiator at a first distance from the first radiator, and the second resonance structure is electromagnetically coupled to the second radiator at a second distance from the second radiator.