The calculation formula for the shape of tapered fibers in movable large-zone furnace fiber-tapering system is derived by the discrete deducing method. We analyze the influences of some setting parameters of the movable large-zone furnace fiber-tapering system, such as moving distance, moving speed of the furnace and moving speed of the holders, on the shape of tapered fibers. The impact to the shape of the fiber waist is discussed primarily. It is found that the furnace moving distance affects the fiber waist length and radius greatly, while the moving speed of the furnace and the holders can effect the fiber waist radius visibly. However, both the speed of the furnace and the holders cannot affect the fiber waist length obviously. All these results are important for the large-zone furnace fiber-tapering technology.