With the intensification of global climate change and environmental pollution, building a clean energy supply system and promoting green energy transformation have become a consensus of the international community. As a major energy consumer, China is actively and steadily advancing its carbon peaking and carbon neutrality goals. The low-carbon transformation of the power industry, one of the main sources of carbon emissions, is particularly critical. By establishing a carbon emission intensity model for thermal power unit operations and a carbon emission source inventory for multiple types of low-carbon energy generation and electrochemical energy storage, a unified carbon footprint accounting model for the power supply side was formed. On this basis, a low-carbon operation simulation method for new power systems that is adapted to the flexible interaction of sources, grids, loads, and storage was proposed along with a calculation method for inter-regional carbon transfer, enabling the simulation and calculation of carbon emissions from the source-side operation of power systems. Taking typical power grids in sending and receiving regions in China as examples, quantitative assessment and analysis of carbon emissions in interconnected power grids was carried out. The research results show that through cross-regional integration of power resources, the total annual operating carbon emissions of the power grids in sending and receiving regions decreased by 0.4%, and the utilization rate of renewable energy increased by 1.4%. After optimizing the power supply operation mode with the goal of minimizing carbon emissions, the total annual operating carbon emissions of the power grids in sending and receiving regions decreased by 7.8% and 11.2%, respectively, which is superior to an optimization method with the goal of maximizing renewable energy consumption.This study provides quantitative assessment tools for energy conservation, emission reduction, and low-carbon operation of power systems, and offers operable implementation methods and technical support for the low-carbon transformation of the power industry.