The design of CBAM, which replaces the carbon emission difference with the carbon price difference between the exporting country and European Union, has greatly weakened the direct emission reduction effect of BCA and the emission reduction incentive function for the the the exporting countries, and its carbon price composition and responsibility arrangement reflect the nature of its unilateral trade measures. As a carbon pricing tool in collaboration with EU-ETS in the EU’s emission reduction actions, there are problems with both the structure and function of the CBAM, and the two types of problems are interlinked and interact with each other, which makes the emission reduction efficiency of the CBAM and its positioning seriously “broken”.The environmental exception clause of GATT and the common but differentiated responsibilities under the UNFCCC framework wouldn’t be the basis for the legitimacy of CBAM, which has failed to make a fairer and more pragmatic arrangement based on the common but differentiated responsibilities of developed and developing countries in the climate issue, and the international community should actively explore the restructuring of the function of the BCA under the ICPF principle in order to safeguard the broader common interests in the climate issue. The exemption clause reveals the EU’s ambition to dominate the international carbon market. Developing countries should make full use of the relevant provisions of international law and actively improve their national emission reduction systems and related legal systems, so as to take more initiative in the international carbon market in the future.