The invention relates to an adjustable anti-galloping spacer for overhead transmission lines, which comprises sub-wire spacers, wherein the sub-wire spacers are installed on both ends of a compound insulator, and each sub-wire spacer is composed of a spacer body and a wire clamping head; the inner ring of the spacer body is provided with a cross beam; the middle of the cross beam corresponds to one wire clamping head; the plane of the cross beam is symmetrically provided with a locating hole I by using the axial line of the wire clamping head as the center; both ends of the compound insulator are respectively fixed with a lambdoidal connecting plate; both ends of each connecting plate are respectively hinged with an adjusting plate I; the adjusting plate I is provided with an elongated adjusting hole; every two adjusting plates I are connected with an adjusting plate II and meshed with each other through a rack; each adjusting plate II is provided with a mounting hole I corresponding to the locating hole I; and the locating hole I in the cross beam, the adjusting hole in the adjusting plate I and the mounting hole I in the adjusting plate II are fixed by bolts. The invention can realize stepless regulation of sub-wire space, and has the advantages of high safety, convenient installation, wide application range and the like.