A phase shifter (100, 300, 500, 700), comprising a cavity, a metal strip line, and a tuning accessory, wherein the metal strip line is located in the cavity, the tuning accessory comprises a fixing portion and a tuning portion connected to the fixing portion, and the fixing portion is configured to be fastened to the cavity; the tuning portion is located in the cavity, the tuning portion is partially or completely opposite to the metal strip line, and a projection of a part that is of the tuning portion and that is opposite to the metal strip line is located on the metal strip line; and the tuning portion is configured to be used to tune the input impedance of a port of the phase shifter, wherein one of a)-d): a) the tuning portion is a metal sheet and the metal sheet is spaced from the metal strip line, or the tuning portion is a dielectric slab and the dielectric slab at least partially covers the metal strip line or is spaced from the metal strip line;, and a side wall of the cavity is provided with a tuning hole, a first end of the fixing portion is connected to the tuning portion, and a second end opposite to the first end is located in the tuning hole; and the second end of the fixing portion is configured to be moved in a length direction of the tuning hole before the fixing portion is fastened to the cavity to drive the tuning portion to move relative to the metal strip line; b) the tuning portion is a metal sheet and the metal sheet is spaced from the metal strip line, or the tuning portion is a dielectric slab and the dielectric slab at least partially covers the metal strip line or is spaced from the metal strip line; and the fixing portion comprises a rotating shaft, an axis of the rotating shaft is perpendicular to a plane on which the metal strip line is located, and the rotating shaft is configured to be rotated before the fixing portion is fastened to the cavity, to drive the tuning portion to rotate relative to the metal strip line; c) a cavity wall (10a, 10b) of the cavity is provided with a plurality of openings spaced apart, the phase shifter comprises at least one tuning accessory, and the at least one tuning accessory is disposed in one or more of the plurality of openings; and the tuning accessory is a dielectric block, and a dielectric constant of the dielectric block is greater than that of air; d) wherein an open-circuit line extends on the metal strip line, one end that is of the open-circuit line and that is away from the metal strip line is a free end, the tuning portion is formed of a dielectric material, the tuning portion is sleeved on the open-circuit line from the free end, and a length of the open-circuit line is less than or equal to a length of the tuning portion; and a cavity wall of the cavity is provided with a tuning hole, and the fixing portion is configured to be moved in an extension direction of the tuning hole before being fastened to the cavity, to drive the tuning portion to move relative to the open-circuit line. a) the tuning portion is a metal sheet and the metal sheet is spaced from the metal strip line, or the tuning portion is a dielectric slab and the dielectric slab at least partially covers the metal strip line or is spaced from the metal strip line;, and a side wall of the cavity is provided with a tuning hole, a first end of the fixing portion is connected to the tuning portion, and a second end opposite to the first end is located in the tuning hole; and the second end of the fixing portion is configured to be moved in a length direction of the tuning hole before the fixing portion is fastened to the cavity to drive the tuning portion to move relative to the metal strip line; b) the tuning portion is a metal sheet and the metal sheet is spaced from the metal strip line, or the tuning portion is a dielectric slab and the dielectric slab at least partially covers the metal strip line or is spaced from the metal strip line; and the fixing portion comprises a rotating shaft, an axis of the rotating shaft is perpendicular to a plane on which the metal strip line is located, and the rotating shaft is configured to be rotated before the fixing portion is fastened to the cavity, to drive the tuning portion to rotate relative to the metal strip line; c) a cavity wall (10a, 10b) of the cavity is provided with a plurality of openings spaced apart, the phase shifter comprises at least one tuning accessory, and the at least one tuning accessory is disposed in one or more of the plurality of openings; and the tuning accessory is a dielectric block, and a dielectric constant of the dielectric block is greater than that of air; d) wherein an open-circuit line extends on the metal strip line, one end that is of the open-circuit line and that is away from the metal strip line is a free end, the tuning portion is formed of a dielectric material, the tuning portion is sleeved on the open-circuit line from the free end, and a length of the open-circuit line is less than or equal to a length of the tuning portion; and a cavity wall of the cavity is provided with a tuning hole, and the fixing portion is configured to be moved in an extension direction of the tuning hole before being fastened to the cavity, to drive the tuning portion to move relative to the open-circuit line.