A high voltage transformer for controlling inductance leakage used for a multiple lamp driving system includes at least one wire frame, a first winding, a second winding, a first magnetic unit, and a second magnetic unit. There is a receiving space in the wire frame for receiving the first magnetic unit, and a first region and a second region is formed on its surface. The first winding and the second winding are individually wound at the first region and the second region. The second magnetic unit is covered on the side of the wire frame. On an appropriate location of the bottom of the second magnetic unit, a transverse beam extends. Thereby, the transverse beam fully separates the low voltage magnetic flux path produced on the first magnetic unit by the first winding and the second winding and the high voltage magnetic flux path produced by the AC.