Abstract: This paper introduces the great risk of reverse power transmission endangering people and equipment in the fault diagnosis of DC test transmission instrument, and analyzes the relevant reasons. Using the one-way conduction principle of high-voltage diode, it is installed in the outgoing line of DC test transmission instrument to realize anti reverse power transmission. It can effectively prevent personnel casualties and equipment damage caused by reverse power transmission of the line. It is easy to operate by adding a new clamp at the end of the outgoing line of the DC test transmitter. It is convenient for the operation of insulated operating lever. There is no need for individual support in the experiment. It realizes the advantages of avoiding direct contact with the line, requiring less time for the experiment, and having a wide range of applications.