The role of ocean carbon sinks in global climate change mitigation and carbon neutrality is still affected by lack of research. Aiming at overcoming the present limitations, a comprehensive and holistic framework and accounting method of ocean carbon sink evaluation are proposed in this study, which consider both carbon sink types and their characteristic carbon storage cycle timescales. The results show that (1) China's total ocean carbon sink is 69.83-106.46 Tg C/year, among which the mariculture, coastal wetlands, and offshore carbon sinks are 2.27-4.06, 2.86-5.85, and 64.70-96.55 Tg C/year, respectively; (2) ocean-based solutions such as coastal protection and restoration, mariculture development, ocean alkalization, ocean fertilization, and marine bioenergy with carbon capture and storage have substantial mitigation potential, but further investigation is required before large-scale deployment; (3) although China's ocean carbon sinks only counterbalanced 3.27-4.99% of its fossil fuel emissions, their tremendous enhancing potential and specific advantages cannot be ignored, and enhancing measures must be taken according to regional characteristics; (4) some uncertainties and limitations still exist, and problems such as double counting, carbon sink offset, and so forth need to be further considered. In a word, this study provides a basis for the development of ocean-based solutions on closing climate mitigation gaps.