The control of greenhouse gas is arguably the most challenging environmental policy issue facing China and other countries. CO_2 is considered to be the major greenhouse gas (GHG) contributing to global warming. Ocean is the largest active carbon pool, and plays an important role in globe climate change. And it is of great significance in the global carbon cycle to accurately estimate the absorbance,transformation,deposition rate of the carbon element in the marine ecosystem. In general,the air-sea CO_2 exchange fluxes were estimated from CO_2 partial pressure between the atmosphere and surface seawater, the primary productivity of phytoplankton was calculated by use of the biogeochemical models based on chlorophyll concentrations in the sea,particle organic carbon (POC) export fluxes in the euphotic zone were derived with ~(234)Th~(238)U disequilibrium in the upper water column, and the organic carbon deposition rate was measured from ~(210)Pb specific activity vertical distribution in the sediment, respectively. Improvements in knowledge of the magnitude of this oceanic carbon uptake can be made thanks to an emerging international observation network that allow routine monitoring of the oceanic CO_2 uptake, on decadal and basin scales. However, not all uncertainties have been resolved, and the high variability of oceanic environments means that a unified description of marine carbon sequestration cannot yet be achieved. For example, there is no invaluable information to illustrate the mutual influence on carbon exchange flux in different medium of the atmosphere, sea water, and sedimentation, respectively, although the amount of carbon sequestration had been investigated in the single medium. There is unclear knowledge to indicate the key factors controlling carbon cycle process in the whole system, which includes the air-sea CO_2 exchange,the primary productivity of phytoplankton in the sea, POC export in the euphotic zone, and the organic carbon deposition in the sediment. It would be extremely challenging to quantify with acceptable accuracy the carbon sequestration in the ocean on a long term basis,and to adequately monitor unintended impacts over large space and time-scales. So,meaningful projections of future behavior of the oceanic sink are more challenging. Attempts to set a baseline stabilization target for the atmospheric CO_2 concentration will ultimately depend on an improved understanding of the oceanic mechanism regulating CO_2 uptake and the ability to make useful predictions of this parameter. To further improve the carbon sequestration assessment method in marine ecosystem, the comprehensive knowledge is required to form the assessment system that consists of the observation techniques, analysis method and the amount of carbon sequestration estimate. Furthermore, the index, criterion and standard, as well as evaluating the standard system of carbon sequestration in the marine ecosystem should be addressed in order to meet the demand of carbon reduction and carbon sink increase in China.