The invention belongs to the technical field of aerospace, and relates to a sealing device of an electric heat transfer test pipe fitting used in an ultralow temperature fluid test system. The sealing device connects the electric heat transfer test pipe fitting and the test system through a flange component, and meanwhile a sealing pad used for sealing is installed between an outer flange plate and an inner flange plate of the flange component. Particularly, in order to ensure using safety, the sealing device is further provided with an insulation disc and an insulation casing pipe which can prevent electric leakage.