Thaliaceans are important group of gelatinous zooplankton that are globally distributed. They are crucial component of the biological carbon pump and marine ecosystem for they can form dense swarms with high feeding rates and producing large amounts of fecal pellets and carcasses. The contribution of thaliacean swarms to the downward transport of carbon depends not only on their abundance but also on their body size. However, the key factors influencing the distribution of different-sized thaliaceans remain unstudied. This study analyzed the thaliacean distribution and associated environment factros in the South China Sea among three different monsoon periods. The results revealed that current velocity and temperature were key factors that affected the distribution of different-sized thaliaceans. This study suggest that global warming-induced changes in surface current velocity and temperature may alter the zoogeographical distribution and abundance of thaliaceans with different sizes, thereby affecting the biological carbon pump and surrounding marine ecosystem.