Beibu Bay , located at the north-west part of South China Sea, is an important fishing area in China. From Feb. 1998 to May 1999 and Nov. 2001 to Jun. 2002, six cruises for the ecological survey were carried out in this area. Samples of zooplankton were co llected to study their distribution and the other biological and ecological aspects. In order to understand the Chaetognatha community in Beibu Bay, the cluster analysis was used in our data analysis. Using the sampling stations as the variable of cluster, the Chaetognatha of Beibu Bay could be treated as one stable community . To further understand the changing pattern of the Chaetognatha community, the species of Chaetognatha was also used as the variable of cluster . The results showed that the species of Chaetognatha o ccurred in Beibu Bay could be divided into three groups, with two main and one subordinate group. The group I was compo sed of Sagitta bedoti , Sagitta enflata, Sagitta neglecta, Sagitta ferox and Krohnitta pacif i. These species could be categorized as the warm water coastal and warm water eurytopic species. They were widely distributed in this area with high o ccurrence and abundance. However, the suitable ranges of salinity and temperature for this gro up species were relative narrow . The occurrence of these species was probably closely related to the existing of the co astal water mass ( with high temperature, low salinity ) . The group ? was composed of Sagitta regularis , Sagitta p acifica, Sagitta robusta and Pterosagitta draco , these were ocean warm-water and warm water eurytopic species. However, the ocean warm-water species are more common in this area. Compared with group . species, the group ? species had relatively wider ranges for salinity and temperature. Their distribution was probably related to water mass in the offshore area ( with high temperature, high salinity) . The group ? species was not widely distributed as the group . did and their o ccurrence and abundance was low. Sagitta delicata, Sagitta minima and Krohnitta subtilis were classified as group ? . They were o cean warm-water and warm water coastal species. However, the former was more important in this area. The distributed area of group ? was small and scattered. The o ccurrence and abundance were the lowest among all groups.