As renewable energy generation and ultra-high-voltage (UHV) transmission technologies continue to advance, long-distance power transmission is increasingly reshaping energy allocation and household welfare. Using data from the China Family Panel Studies (CFPS) and a stacked difference-in-differences (stacked DID) approach, this study examines the impact of UHV transmission projects on household energy poverty and explores the underlying channels. The results show that UHV projects significantly alleviate household energy poverty, and the findings remain robust across a series of robustness checks. Heterogeneity analysis indicates that the poverty-reducing effect is stronger for low-education households, low-income households, and households with elderly members, suggesting that UHV projects disproportionately benefit more vulnerable groups. We further find that UHV projects transmitting clean or mixed electricity have a stronger effect than those relying mainly on thermal power. Furthermore, the beneficial impact of UHV projects appears to be more pronounced under heightened geopolitical risk and uncertainty. The mechanism analysis suggests that UHV projects alleviate energy poverty primarily by expanding employment opportunities, facilitating labor reallocation away from agricultural activities, and reducing household electricity expenditure. These findings highlight the welfare implications of large-scale transmission infrastructure and suggest that grid integration can serve as an important policy instrument for simultaneously advancing energy security, clean energy transition, and energy poverty reduction.