The present invention provides a primary high-voltage circuit cleaning agent, which comprises the following compositions in percentage by mass: 1 to 20 percent of polyethylene glycol octyl phenylether, 1 to 20 percent of nonylphenol polyoxyethylene ether, 1 to 3 percent of n-propyl bromide, 10 to 20 percent of C2Cl3H3, and 5 to 60 percent of C3HCl2F5. The invention also provides a method for preparing the primary high-voltage circuit cleaning agent, which comprises the step of placing the components into a closed container in proportion to react for one hour at the temperature of between 20 and 30 DEG C under normal pressure. The cleaning agent has no environment pollution, low corrosivity, strong physical decomposition capacity, and safe and reliable use, and can quickly and thoroughly eliminate dust, oil stain, carbon residue, salinity, humidity, metal dirt and various charged particles on the surfaces and deep layers of various precision equipment circuits, effectively eliminate 'soft fault', ensure the best working state of equipment and reduce the maintenance cost.