A phase shifter, comprising a cavity and a first fixed transmission line, a second fixed transmission line, and a slidable transmission line that are located in the cavity; wherein • the first fixed transmission line is provided with a first open slot, the second fixed transmission line is provided with a second open slot, and opening directions of the first open slot and the second open slot are opposite to each other; and • two ends of the slidable transmission line are respectively clamped in the first open slot and the second open slot, so that the slidable transmission line is electrically connected to the first fixed transmission line and the second fixed transmission line, and the slidable transmission line slides relative to the first fixed transmission line and the second fixed transmission line, • wherein the slidable transmission line comprises a dielectric substrate, a first phase-shift circuit and a second phase-shift circuit, wherein the first phase-shift circuit is disposed on a first surface of the dielectric substrate and the second phase-shift circuit is disposed on a second surface of the dielectric substrate, the first surface and the second surface are surfaces which tightly couple the dielectric substrate and the first open slot and the second open slot, and the first surface and the second surface are disposed opposite to each other, • wherein the dielectric substrate is provided with a through hole and the through hole also extends through the first and second phase-shift circuits (203, 204), wherein an inner wall of the through hole is coated with a metal layer, • wherein a first metal ring of a preset width is disposed at a first edge of the through hole and a second metal ring of the preset width is disposed at a second edge of the through hole, wherein the first metal ring, the second metal ring and the through hole are concentric and coaxial, and the first metal ring and the first phase-shift circuit are connected and the second metal ring and the second phase-shift circuit are connected, wherein the first phase-shift circuit on the first surface is connected to the second phase-shift circuit on the second surface by using the metal layer and the first and second metal rings. • the first fixed transmission line is provided with a first open slot, the second fixed transmission line is provided with a second open slot, and opening directions of the first open slot and the second open slot are opposite to each other; and • two ends of the slidable transmission line are respectively clamped in the first open slot and the second open slot, so that the slidable transmission line is electrically connected to the first fixed transmission line and the second fixed transmission line, and the slidable transmission line slides relative to the first fixed transmission line and the second fixed transmission line, • wherein the slidable transmission line comprises a dielectric substrate, a first phase-shift circuit and a second phase-shift circuit, wherein the first phase-shift circuit is disposed on a first surface of the dielectric substrate and the second phase-shift circuit is disposed on a second surface of the dielectric substrate, the first surface and the second surface are surfaces which tightly couple the dielectric substrate and the first open slot and the second open slot, and the first surface and the second surface are disposed opposite to each other, • wherein the dielectric substrate is provided with a through hole and the through hole also extends through the first and second phase-shift circuits (203, 204), wherein an inner wall of the through hole is coated with a metal layer, • wherein a first metal ring of a preset width is disposed at a first edge of the through hole and a second metal ring of the preset width is disposed at a second edge of the through hole, wherein the first metal ring, the second metal ring and the through hole are concentric and coaxial, and the first metal ring and the first phase-shift circuit are connected and the second metal ring and the second phase-shift circuit are connected, wherein the first phase-shift circuit on the first surface is connected to the second phase-shift circuit on the second surface by using the metal layer and the first and second metal rings.