Conventional reliability assessments of transmission towers using standard calculation formulas usually neglect corrosion-induced performance degradation, and the recommended range of wind load effect ratios is typically subjective. To address these limitations, this study focuses on service towers and proposes a time-dependent reliability analysis method under wind load within the framework of the standard formula. First, a resistance degradation model considering corrosion effects is developed by integrating environmental conditions and material type into the corrosion rate. Second, the wind load effect ratio is used as a random variable and its statistical characteristics are obtained by distribution fitting using real tower monitoring data. Third, the equivalent normalization (JC) method is used to calculate the reliability index of the service tower based on the standard formula. Finally, the sensitivity of the reliability index to key parameters in the standard formula is quantitatively evaluated. Results show that the wind load effect ratio approximately obeys a generalized extreme value distribution and exhibits strong correlation with tower reliability. Moreover, member initial thickness, atmospheric corrosivity and wind load adjustment coefficients all significantly influence reliability evolution. Specifically, higher atmospheric corrosivity accelerates reliability degradation, while the influence of corrosion decreases as member initial thickness increases. Additionally, a higher wind load adjustment coefficient corresponds to a higher reliability index.