The invention discloses a transformer on-load voltage regulation device and method. The device comprises a compensation winding, a current transformer and a controller, wherein the compensation winding is located on the low-voltage side of a transformer and connected with a primary winding of a coupling transformer in parallel, a secondary winding of the coupling transformer is connected with a low-voltage winding of the transformer, the compensation winding changes the tapping and changes the voltage ratio of the compensation winding according to a control instruction of the controller, thereby changing the voltage of the secondary winding of the coupling transformer and adjusting the voltage of the output end of the transformer, the current transformer is connected to a low-voltage winding circuit of the transformer in series and used for monitoring a load current, and the controller is used for sending a control instruction to change the tapping and switch off a load tapping switchwhen the load of the transformer changes and the load current and a preset current threshold are not consistent. By means of the device, the actions of the load tapping switch can be realized at low voltage level and low working current, voltage compensation is conducted on the voltage of the low-voltage side of the transformer, and the working voltage level of the load tapping switch is reduced.