To balance the requirements of structural safety and economic efficiency in transmission tower design, this study proposes a structural optimization method based on an Improved Sparrow Search Algorithm (ISSA). Specifically, the methodology integrates Circle chaotic mapping to initialize the sparrow population distribution, followed by the introduction of a firefly perturbation strategy. This strategy updates the sparrow positions derived from the basic algorithm, thereby enhancing the algorithm’s ability to escape local optima. Based on these enhancements, a mathematical model for structural optimization is established with the primary objective of minimizing the total weight of the tower. The penalty function method is employed to handle constraints, while the finite element method is utilized for internal force analysis. To verify the effectiveness of the proposed approach, a typical cat-head transmission tower is selected as a case study. The optimization results obtained from the ISSA are compared with those produced by the Daoheng software, demonstrating a weight reduction of 3.79%. These findings indicate that the ISSA effectively improves the optimization performance and provides an efficient solution for the preliminary sizing design of transmission towers.