Silver nanowires (AgNWs) are promising materials in the fabrication of flexible and transparent conductive thin films (FTCFs), which are key components of flexible optoelectronic devices. However, the performance of AgNW FTCFs is severely limited by their low aspect ratio, and the fabrication of AgNWs with a high aspect ratio remains a significant challenge. In this study, AgNWs with a diameter of 40 nm and aspect ratio of 2000 were synthesized rapidly by controlling the total molar concentration of Cl⁻ ions in the reaction solution by a typical polyol method to adjust the Cu²⁺/Fe³⁺ molar ratio. Subsequently, AgNW FTCFs were fabricated by the coating method using hydroxyethyl cellulose (HEC). The films exhibited a low sheet resistance of 68 Ω/sq and transmittance of 86.70%, which are comparable to those of typical indium tin oxide electrodes. Meanwhile, a mechanical robustness test showed that the sheet resistance of the AgNW-HEC films increased by only 3.15% even after 3000 bending cycles.