A rectification-bridge type over-voltage suppression equipment can significantly suppress over-voltage occurred duringa no-load electric furnace transformer interrupting. However， the mechanism and application of the equipment have not beensystematically analyzed. Based on electromagnetic transient analysis， over-voltage suppression mechanism of the equipment isanalyzed. The equipment absorbs electromagnetic energy stored in the circuit with high-capacity electrolytic capacitor aftercurrent chopping， and the over-voltage is also limited by small leakage inductance of the transformer winding. In typicalcondition， the over-voltage can be limited to 1.15 rated. In addition， an estimation formula of over-voltage is derived as well.The main influencing factors， such as short circuit impedance， capacity， chopping current， and terminal-to-earth capacitance ofthe transformer， to the over-voltage are evaluated， It is concluded that the less the short circuit impedance or the larger thecapacity of the transformer， the smaller the over-voltage.