The invention relates to an adjustable shielding frame for improving a peripheral power frequency electric (magnetic) field of an overhead transmission line. The adjustable shielding frame comprises fence fixing rods (1) and vertical fixing rods (4), wherein more than two fence vertical rods (3) and two vertical fixing rods (4) are respectively, vertically and fixedly arranged on a roof (11), the upper ends of the vertical fixing rods (4) are provided with vertical movable rods (5), and a shielding net fixing rod (6) and a shielding net telescopic rod (7) are respectively arranged between the adjacent two vertical fixing rods (4) and between the adjacent two vertical movable rods (5) and are connected in a sliding manner. The adjustable shielding frame disclosed by the invention has the advantages of simple structure and large adjustment range; and different installation environments are met by adjusting the lengths of the fence movable rods, the vertical movable rods and the shielding net telescopic rods, the electromagnetic shielding effect is excellent and the application range is wide.