The invention, which belongs to the technology field of the tool die utilized for the optical and electrical cable process, relates to a die utilized by a longitudinal covering process of a glass fiber tape. The die comprises a conduit and a matched joint; there is a through hole in the center along the length of the conduit; the matched joint is fixed at one end of the conduit and a narrowed step is formed at one end of the matched joint; and a step external thread is arranged at an outer wall of the narrowed step. Advantages of the die provided in the invention are as follows: a longitudinal covering quality can be ensured; the die enables an extruding machine to be able to flexibly cope a cable core extrusion outer sheath that is used for covering longitudinally or winding a glass fiber tape.