Abstract: Against the background of intensifying global climate change, fully utilizing the efficient carbon sink function of seaweed cultivation is an important way to achieve China’s “double carbon” goals. To maximize the potential of seaweed cultivation as a carbon sink, it is essential to calculate the carbon sequestration capacity of seaweed cultivation scientifically, accurately, and systematically. Regrettably, previous studies on the carbon sink of seaweed cultivation had largely overlooked the critical contributions of lost particulate organic carbon (POC) and released refractory dissolved organic carbon (RDOC) during the cultivation process. Based on the production data of seaweed cultivation from nine coastal provinces of China from 2000 to 2022, considering the carbon sequestration formed by the release of POC and RDOC during seaweed cultivation, the long-term and short-term carbon sinks of seaweed cultivation in China was evaluated in this paper. The results showed that the average production of seaweed cultivation in coastal provinces and cities in China from 2000 to 2022 was 18.2×10⁵ t·a⁻¹, with an average cultivation area was 11.1×10⁴ hm²·a⁻¹. The average long-term carbon sink of seaweed cultivation in China was 2.70×10⁵ t(C)·a⁻¹, the average short-term carbon sink was 4.75×10⁵ t(C)·a⁻¹. The average total carbon sink (long-term carbon sink + short-term carbon sink) was 7.45×10⁵ t(C)·a⁻¹, and the carbon sink of seaweed cultivation in China was expected to increase year by year. It is estimated that the total carbon sink of seaweed cultivation in China will reach 14.22×10⁵ t(C) by 2030. In terms of total carbon sinks, long-term carbon sinks and short-term carbon sinks, Fujian, Shandong and Liaoning provinces contributed about 95.5% of the carbon sinks, with the greatest increase observed in the southern marine economic circle. The carbon sink of seaweed cultivation in nine coastal provinces in China showed significant differences due to cultivation varieties, aquaculture production and other reasons. Kelp had the highest carbon sequestration capacity among the seaweed species, and compared to other seaweeds, it required the smallest cultivation area to achieve China's “carbon neutrality” goals. Based on calculations of long-term carbon sink, short-term carbon sink, and total carbon sink, the required cultivation area for kelp to achieve China’s “carbon neutrality” goals was estimated to be 1.14×10⁷ hm², 0.65×10⁷ hm² and 0.41×10⁷ hm², respectively. According to the coastal seaweed production, the annual average removal of carbon, nitrogen, and phosphorus by seaweed cultivation from 2000 to 2022 was estimated at 7.45×10⁵ t(C)·a⁻¹, 5.44×10⁴ t(N)·a⁻¹, and 6.59×10³ t(P)·a⁻¹, respectively. Furthermore, the release of oxygen was estimated at 1.99×10⁶ t(O₂)·a⁻¹, and the total environmental benefits of coastal seaweed cultivation in China reached 173.03 billion CNY in 2022. The results of this study provide important insights into the development of seaweed cultivation in the context of achieving “carbon neutrality” and mitigating seawater deoxygenation and eutrophication.