The utility model relates to a power engineering technology field especially relates to an automatic steady voltage and dynamic reactive compensation's transformer. The utility model discloses a single phase transformer's secondary winding and the 2nd single phase transformer's secondary winding series connection are between two power output ends, phase 1 enzyme power input end, phase 2 enzyme power input end, three phase current input are a plurality of access primary windings, and the point the that wherein number of turns is maximum is the coil number of the normal during operation of voltage, the utility model discloses a fabric one -tenth is organized including connection capacitor bank's N way contactor group and thyristor to the dynamic reactive compensation circuit, and each way contactor component do not comprises selection contactor and execution contactor, all selection contactor inputs link together and constitute the switching generating line. The utility model discloses it is simple to have the voltage switching circuit, and the in -process voltage output that steps up or step down is stable, and automatic voltage regulation and dynamic reactive compensation circuit autonomous working separately, does not influence mutually, has ensured the normal work of whole circuit.