Abstract: Coal-bioenergy co-firing with carbon capture and storage（CBECCS） has emerged as a key technological option for deep decarbonization and low-carbon transition in China’s coal-fired power sector due to its significant emission reduction potential. However, the existing carbon emission reduction accounting frameworks are primarily designed for conventional CCS projects and lack a dedicated methodology for CBECCS, making it difficult to quantify its mitigation benefits and hindering policy support and large-scale deployment. Accordingly, it is imperative to establish a scientifically robust and comprehensive carbon emission reduction accounting methodology for CBECCS to facilitate its large-scale deployment. This study adopts a full process perspective to systematically construct a carbon emission reduction accounting model applicable to CBECCS technology, establishing three core modules: baseline emissions, project emissions, and leakage emissions. The research fully considers the carbon-neutral characteristics of biomass fuels and proposes a baseline emission construction method based on carbon contribution ratio allocation. The study clearly defines accounting boundaries, identifies emission sources in fuel acquisition, carbon capture, transportation, storage, and facility activities, and develops a phased estimation method for leakage emissions to construct a comprehensive net emission reduction accounting model. Based on this model, the study analyzes key factors affecting CBECCS carbon accounting, focusing on biomass co-firing ratios and resource availability, storage stability, and negative emissions. A case study conducted on Unit X, a 600 MW coal-fired power plant, demonstrates that with a biomass co-firing ratio of 25 % （on an energy basis）, the annual net CO₂ emission reduction of the CBECCS project reaches 1.352 1 million tons, validating the significant reduction potential of this technology pathway. This research provides methodological support for carbon emission reduction accounting in CBECCS projects under multi-stage and multi-source emission scenarios, offers a feasible quantitative basis for CBECCS technology to enter carbon trading markets, and promotes its application in China’s coal-fired power industry’s negative emission technology system.