Abstract: During long-term operation of the COT type bushing of the main transformer, oil leakage may occur due to the aging of the sealing rubber ring of the oil drain valve. Long term leakage may lead to hidden dangers such as water seepage inside the bushing. For the same type of bushing, all oil samples need to be taken for inspection. To take oil samples, the rainproof cover of the bushing needs to be removed first. At present, a belt wrench is used to disassemble and assemble the COT sleeve rain cover. However, when using a belt wrench, the fixed screw teeth of the rain cover are often misaligned due to force, and the sliding teeth cannot be removed. The sleeve needs to be replaced after violent damage. To solve the above problems, this study designs a specialized disassembly and assembly tool for rain covers. This tool can directly act on the fixed screw teeth of the casing rain cover for disassembly and assembly, making it convenient for COT casing to take oil samples for hazard investigation.