The invention discloses a special online fixing tool for an inlet guide vane of a circulating nitrogen compressor. The special online fixing tool comprises a rear end blocking plate, a front end blocking plate and a ratchet wrench, wherein a handle is arranged at one end of the ratchet wrench; the front end blocking plate is arranged on the middle-end part of the handle; a nut is arranged on the front-end blocking plate; a matched fixed bolt is arranged in the nut; the rear end blocking plate is arranged at the tail end of the handle; and the rear end blocking plate is movably connected with the handle through a cylindrical pin. The special online fixing tool realizes online replacement, modifies the possibility of a locator, is safe and reliable in design, provides solid technical guarantee for enterprise production, equipment maintenance, safe management and the like, saves a great deal of production and maintenance cost, and eliminates hidden danger generated by factors such as a plurality of defects in design, manufacturing and the like of equipment to certain extent.