In order to investigate the carbon sink mechanism of marine aquaculture， the carbon sink of shellfish and algae aquaculture was taken as the research object， and four efficiency analysis models were applied to evaluate the carbon sink efficiency of shellfish and algae aquaculture in the coastal areas of China. The results of the study show that among the coastal areas， the shellfish and algae farming process in Liaoning Province not only pays attention to the efficiency value of practical production， but also pays more attention to the realistic degree of the effect of the actual input and output process than other regions， which can bring the "ecological-economic-social" benefits of removable carbon sinks into full play， and has a certain demonstration effect for other regions； In Guangxi， there is a serious imbalance between the scale of labor input and the scale of land input， which corresponds to the input and output of shellfish aquaculture with "high efficiency and low effectiveness"， and the management of its professional practitioners is inefficient； in Hainan Province， the output rate of shellfish carbon sinks is very limited， and the function of carbon sinks generated by shellfish aquaculture makes very little economic， social and ecological contribution to Hainan Province. The economic， social and ecological contribution of shellfish aquaculture to Hainan Province is negligible. In addition， based on the public weighting method of input-output scale， the allocation scheme of the initial CO₂ absorption credit in shellfish aquaculture in China is proposed. The marginal contributions of this paper lie in the following. Firstly， applying the performance-based integrated efficiency model to the measurement of shellfish aquaculture carbon sinks for the first time makes the value of carbon sinks can take account into both efficiency and effectiveness. Secondly， it proposes the carbon absorption quota of shellfish aquaculture carbon sinks from the perspective of input-output scale based on the public weighting approach. Thirdly， it incorporates the efficiency factor into the carbon absorption quota by means of the public weighting approach， and allocates carbon absorption quota with the combination of input-output scale and efficiency. it supplements the new allocation method based on DEA. The research has certain policy significance for the development of fishery carbon sinks in China's coastal areas and the improvement of the carbon trading market mechanism.