The invention discloses a remanence evaluating and demagnetizing device of a power transformer. In a main circuit, two ends of a switch power are respectively connected with a filter capacitor and a resistor R0 in parallel, a forward end of the switch power is connected with a main switch T5 in serial, a switch T6 and a resistor R1 serial branch, a switch 1 and a switch 2 serial branch, a switch 3and a switch 4 serial branch are connected at the rear end of the main switch T5 in parallel, a drive circuit is connected with drive ends of the main switch T5, the switch T6, the switch 1, the switch 2, the switch 3 and the switch 4, and a control circuit is connected with the drive circuit and is used for sending an instruction to the drive circuit. The device provides reference for rapid, accurate demagnetization, is more intelligent, can demagnetize rapidly and thoroughly, and greatly shortens field demagnetization time and improves demagnetization effect.