The utility model relates to the shielding case of a monitoring system circuit for a power transmission line, and particularly provides the shielding case of a windage yaw monitoring system circuit for the insulator chain of a power transmission line, which solves the problems in the prior art that electric conduction paints cannot be recycled to result in contamination and metal shielding boxes are high in cost and erodible. The shielding case is composed of a box body, an insulated shielding layer and an upper cover. The box body is in the shape of a cuboid. The insulated shielding layer is covered on the inner surface of the box body. The insulated shielding layer is orderly composed of a copper wire mesh, a glass fiber layer and a tin-nickle powder coating film from outside to inside, wherein the tin-nickle powder coating film is arranged between the copper wire mesh and the glass fiber layer and is coated on the surface of the glass fiber layer. The upper cover is rectangular. One side of the upper cover is fixedly provided with a sealing gasket, and the four corners of the upper cover are provided with connecting holes. The shielding case is simple in structure, easy to assemble, disassemble and maintain, and good in air tightness. The insulated shielding layer is simple to manufacture, convenient to install, low in cost, reusable and small in environmental pollution. The box body and the upper cover are low in cost and corrosion-resistant.