To explore emission baseline, technically the most difficult issue for Clean Development Mechanism (CDM) project development, as well as to examine whether CDM is a possible way to help Beijing restructure its heating energy consumption, this paper conducts a CDM baseline case study on residential heating in Beijing. Based on investigation, energy consumption forecast and economic analysis of future technology options, the technology benchmark and site-specific baselines for both retrofit projects and new heating projects have been discussed. The results indicate that fuel switching from coal to natural gas can meet the additionality criteria in many cases and will be the main type of CDM project. In addition, it also proves that the technology benchmark and the case-by-case baseline setting approach are applicable for future CDM cooperation projects on heating in Beijing.