The present invention discloses a dustproof device for a transformer and a voltage design method of a dust collecting electrode thereof. The dustproof device comprises a frame, a power box, a dust collecting electrode and a corona electrode. The frame is mounted on a cooler of the transformer; the dust collecting electrode is arranged on the frame and connected with a positive electrode of the power box for adsorbing the dust sucked into the cooler; the corona electrode is arranged on the frame in parallel with the dust collecting electrode, connected with the negative electrode of the power box and is formed by staggered vertical corona wires and transverse corona wires. The invention designs an optimal voltage model of the dust collecting electrode based on the three objectives of electric field strength, dust particle charge and dust removal efficiency; the dust sucked into the cooler can be effectively filtered out; the dust removal effect is improved; and the problem of abnormal heating of the transformer during operation can be effectively solved.