Overhead transmission lines are crucial components of power grid construction, and their carbon emissions significantly impact the low-carbon construction of the power grid. This study adopts a cradle-to-gate life cycle assessment (LCA) method, defining the system boundary as the material production, transportation, and construction phases. Using the carbon-accounting software eFootprint and the emission factor method, we calculate and analyze the carbon emissions of a 500 kV double-circuit overhead transmission line project in Shantou, Guangdong Province, and systematically examine the emission characteristics from material production through construction. Results show that the material production phase dominates the carbon emissions of the project, accounting for 99.82% of the total emissions. Among them, conductors (49.41%) and tower materials (37.28%) are the core sources of carbon emissions, with a combined contribution of 86.69%. The findings highlight conductors and towers as key targets for emission reduction through strategies such as optimized material selection, adoption of high-strength lightweight alternatives, and modular construction techniques. However, this analysis has limitations: it is confined to a single subtropical coastal project, relies on industry-average emission factors from the CLCD database (with inherent methodological uncertainties), excludes operational and end-of-life phases, and should not be generalized without regional validation. While the study identifies key emission hotspots and potential mitigation levers, quantitative low-carbon design guidance requires project-specific data and full life-cycle assessment.

Driven by global carbon neutrality targets, the low-carbon transformation of power systems necessitates rigorous carbon evaluation of grid infrastructure. However, existing assessments of overhead transmission lines often exhibit incomplete life-cycle boundaries and lack a coordinated approach to subjective and objective weight allocation. To address these gaps, this study targets overhead transmission lines and constructs a comprehensive low-carbon evaluation index system comprising 14 indicators across four life-cycle stages, namely design, construction, operation, and recycling. A hybrid evaluation model is proposed based on the combined analytic hierarchy process and entropy weighting method. The analytic hierarchy process is utilized to derive expert-based subjective weights, while the entropy weighting method extracts objective data variations from multiple samples, which are then integrated to obtain robust composite weights. An empirical analysis conducted on a 500 kV double-circuit overhead transmission line project in China validates the proposed framework. The results reveal a comprehensive evaluation score of 80.219, corresponding to a “low-carbon” grade. Moreover, the line loss rate (0.234227), operational carbon emissions (0.133978), and steel consumption per unit length (0.122381) are identified as the pivotal indicators dominating the evaluation outcome. This research provides quantitative support and practical criteria for decision-making regarding low-carbon design, green construction, operational loss reduction, and resource-oriented retirement of transmission line projects.