Abstract: Under the influence of bad weather, dust and moisture accumulation and oil stains and dirt, transformer oil temperature measurement is prone to dial damage, reading errors, inaccurate indicators and other problems. Based on the technical principle of instrument protective cover, this paper designs a magnetic auxiliary protection device for measuring transformer oil temperature. Its box is made of lightweight corrosion-resistant material and painted to prevent rust. A magnetic connector is installed outside the box, which can be adsorbed or clamped with the field device to ensure the stability and reliability of the box cover. It is equipped with a visual window in front of the box, in order to facilitate on-site reading. The device has the advantages of convenient installation, simple operation, low cost and wide application range. It has practical research significance and practical value.