Recently, emerged an easy way to fabricate to a nano fiber-optic sensor (NFOS) using the inscription on the silica fiber. A simple etching reactor was developing to obtain reproducible tapers of desired diameter and length. This approach is reflected on-line monitoring of the etching using the transmitter and receiver system. The experimental data indicate that the diameter of the optical fiber decreases linearly with the time of survival of hydrofluoric acid, and etching was used at room temperature. In this study, we were examined the best rate of etching that used for the fabrication of such sensors. In the aforementioned technique, this method aims to determine the diameter of the reduced core and show the evolution of the two different processes from the nano fiber regime to the fixed regime in which the mode was remote from the surrounding evanescent field, intensity can propagate outside the segment fiber when the core diameter is less than 100 nm. To expire a easy-going has developed the diameter of the fibre after etching to the process has been done successfully.