<p>The work aim is to establish the mechanism of influence of silica glass-based optical fiber drawing temperature on its strength. The object of research was silica fiber of 125&#xa0;μm diameter with a polymer coating of 60&#xa0;μm thickness. The fiber preform, fabricated by the MCVD method, contained a core doped with 3&#xa0;mol % GeO₂ and a cladding containing small additions of P₂O₅ and fluorine. <b>Fiber strength was measured by the two-point bending method.</b> When fiber drawing temperature was decreased from 2150 to 1900&#xa0;°C, its strength degraded from 5.9 to 5.6 GPa. For each fiber drawing temperature, 20 samples were used to evaluate the mean strength value and its standard error (≈ 0.016 GPa). For the first time the nature responsible for the decrease in strength of silica fiber with lower drawing temperatures has been identified. This phenomenon is characterized by a radial viscosity gradient forming in the fiber during drawing. This results in a competition between the elastic deformation of the outer silica glass fiber cladding and the plastic deformation of its inner low-viscosity regions under the influence of the fiber drawing force. A simple mathematical model for estimating the fiber surface stress layer thickness and the magnitude of tensile stresses in it is proposed. Based on the etching rate measurement of the fiber in HF solution, the stressed outer layer thickness of the fiber drawn at 1900 and 1970&#xa0;°C was measured. The calculated and experimental results for the stressed layer thickness agree well.</p> Graphical Abstract <p></p>