The seagrass bed is one of the most productive wetland ecosystems, providing valuable ecological goods and services. About 2%-5% of seagarss populations disappeared each year on Earth, which has been due to a wide variety of human and natural disturbances in recent years. The dynamics of non-structural carbohydrates (NSC) reserves play an important role in determining seagrass growth and its response to environmental disturbances. In order to improve our understanding of the NSC in seagrasses, the information on the NSC responses to environmental stresses, such as light, nutrient, salinity, ocean acidification, temperature, sulfide and animal grazing were summarized. Seagrasses are particularly sensitive to reductions in light availability, where small decreases can cause significant declines in growth and distribution. During periods of reduced photosynthesis caused by light limitation, the stored NSC in belowground tissue can be reallocated to meet the C (Carbon) demand of seagrasses. Thus, seagrass species with higher belowground biomass and carbohydrate storage capacity can tolerate longer period of light limitation. Nitrogen assimilation requires carbon skeletons for the respiratory pathway and reserves. Under excessive nitrogen conditions, carbon requirements for synthesizing amino acids may exceed carbon fixation capacity, leading to a decrease in NSC concentration and NSC reserves reallocation. Under hypo- and hypersaline conditions, a number of organic compounds in seagrass including soluble sugar can be produced in response to salinity stress. Furthermore, carbon skeletons are also important for the synthesis and accumulation of proline (and other nitrogen containing osmotica such as glycine betaine or ectoine) during elevated salinities. Ocean acidification may promote seagrass photosynthesis, resulting in an increase of NSC synthesis in aboveground tissue and transfer to belowground tissue. And the belowground tissues of seagrass became a sink for fixed carbon. The effect of temperature on the NSC accumulation was significant by means of altering seagrass photosynthesis, respiration and nitrogen metabolism. Additionally, the decrease of NSC biosynthesis and reserves was resulted from both sulfide and animal grazing by inhibiting the enzyme activity and grazing seagrass photosynthetic tissue, respectively. Finally, research fields in the future are pointed out including: (1) the transformation mechanism between NSC and structural carbohydrates, and between soluble sugar and starch of seagrass in different life stage (seed dormancy and germination, development and reproduction); (2) the coupling impact of dual and/or more environmental factors on seagrass NSC; (3) the application of NSC as an ecological indicator for evaluating the seagrass ecosystem health evaluation.