In the context of addressing global climate change and advancing the “carbon peak and carbon neutrality” goals, low-carbon transformation of block energy supply systems has become a key pathway to sustainable urban development. This study selects a block in Tianjin as a case study and proposes a multi-measure synergistic assessment method for block energy supply carbon neutrality, integrating load forecasting, energy-saving retrofitting, and renewable energy generation strategies. Firstly, the impacts of various energy-saving measures—such as load reduction, high-performance doors and windows (HDW) installation, energy substitution, and pipeline network planning—on block energy demand were analyzed. Secondly, the contributions of high-biogenic-content waste (HBW) power generation and photovoltaic (PV) power generation to block energy supply carbon neutrality were analyzed. Finally, a comprehensive assessment of carbon neutrality was conducted, along with the calculation of the economic payback period. The results indicate that the contribution of each measure to load reduction follows the order: PV power generation ≫ HBW power generation > HDW installation > energy substitution ≈ load reduction. Renewable energy generation not only offset the remaining carbon emissions during the operational phase of energy supply, but also fed surplus electricity into the grid, contributing an additional 427 tCO<inf>2</inf> of net carbon reduction. Based on the calculation of initial investment and annual net revenue of the multi-measure synergistic approach, the economic payback period of the block energy supply retrofit is 8.24 years. This study provides theoretical support and practical guidance for achieving block energy supply carbon neutrality.