The invention relates to a monopole fault isolation system for a real bipolar flexible DC power transmission project, and the system is characterized in that the system comprises a fault isolation device which comprises a current transformer, a neutral bus region and a neutral line difference protection device disposed on a metal return wire, wherein the current transformer and the neutral bus region are disposed on a neutral bus connected with the MMC lower bridge arms of the pole I and the pole II. The neutral bus region of the pole I comprises a DC change-over switch, two DC disconnecting knife switches, a neutral bus DC voltage between the DC change-over switch and one DC disconnecting knife switch, a monopole neutral bus DC current between the DC change-over switch and the other DC disconnecting knife switch, and grounding knife switches at two sides of the two DC disconnecting knife switches. A pole II protection device and a pole I protection device have the same structure. Theneutral line difference protection device comprises a first disconnecting switch, a second disconnecting switch, and a metal return wire DC current. The first disconnecting switch is grounded througha grounding current of a current convertor station, and one side of the second disconnecting switch is grounded through a grounding switch. The system can be widely used for the real bipolar flexibleDC power transmission project.