The utility model relates to a DC magnetic bias online monitoring and separating device of a power transformer. The DC magnetic bias online monitoring and separating device comprises a separation device and a magnetic bias online monitoring device. The separation device comprises a block condenser C, a voltage-limiting protector FR connected in parallel with the block condenser C, an alternating-current transformer Ta, an AC/DC current transformer Tb and a by-pass switch K. The magnetic bias online monitoring device comprises a by-pass switch Kz1, a digital monitoring device Kz2, a communication terminal WL connected with the output end of the digital monitoring device Kz2, and a isolation transformer GT connected with the by-pass switch Kz1 and the digital monitoring device Kz2. By means of the DC magnetic bias online monitoring and separating device, the voltage class of the block condenser C is reduced, reliability and short-circuit impact resistance of the device are improved, the largest short-circuit impact current can be 125 kA, and the DC magnetic bias online monitoring and separating device can be applied to neutral-point grounding loops of extra-high voltage or extreme-high voltage large or giant transformers; noise of the transformers is effectively lowered, and temperature raising of the transformers is restrained.