The utility model belongs to the technical field of aerospace, and relates to a device for sealing an electric heat-conducting test pipe piece, wherein the device is used in an ultralow-temperature fluid-test system. The device employs a flange assembly to connect the electric heat-conducting test pipe piece with the test system. Meanwhile, a sealing gasket, which is used for sealing, is installed between an outer flange plate of the flange assembly and an inner flange plate of the flange assembly. Especially for guaranteeing the safety of application, the device is also provided with an insulating circle disc and an insulating sleeve which are used for preventing electric leakage.