Abstract: Acid soluble process is an advanced technology for the fabrication of flexible image bundle with fiberizing of the single fiber as the key to the whole process. Triple-crucible method is considered an effective way to produce the quality fiber. In order to ensure the balance amang the core, cladding and acid soluble glass, beginning with the designing of the profile of the single fiber, the working parameters of each of the core, cladding and acid soluble glass were determinated. Based on the experimental data and fluid dynamic principle, the conditions of viscous glass in the crucible tube as well as in the annular gaps of the crucible were studied, and the calculation of the outlet parameters of the crucible was proposed. These parameters were applied in the designing of the crucible and was proved to be feasible.