As the tap-changer of contactless on-load tap-changing voltage for distribution transformer inverse-parallel thyristor is located in 10 kV side of the transformer，while thyristor trigger circuit and control system are in 0.4 kV side.In face of the insulation problem of on-load tap-changing voltage device across the primary and secondary side of transformer，a trigger scheme based on optical fiber insulation is designed，which is via studies on fiber optical communication technology and high voltage side dc conversion circuit，combined with automatically zero-cross operating trigger circuit and its improvement on high voltage withstanding.The feasibility of the principle of optical trigger scheme is verified through parameters design and experiment of hardware circuit.The experimental results show that the scheme can solve the insulation problems of inverse-parallel thyristor trigger in high voltage side of distribution transformer.