In the field of CDM practices, some theories can be used as reference: firstly, the emission trading theory for environmental protection; secondly, the rules formed in the practice of international climate cooperation; thirdly, the CDM requirements and procedures stipulated in the Kyoto Protocol. In a strict sense, these rules do not form a “theory”, as they have certain limitations and need to be revamped. A review or summary of these rules is helpful in understanding the following ideas and analyses, so these rules can be viewed as “theoretic basis”.