Study on how related species coexistence in community is a central objective in ecology. However, knowledge of coexistence pattern of Sagitta bedoti and S. enflata in the Sanmen bay and adjacent waters remains poorly known. Two speciesof S. bedoti and S. enflata with environmental factors were sampled, aiming to elucidate relationships that drive theircoexistence, on August and November of 2019, April and December of 2020, respectively. The Generalized Additive Models(GAMs) was used to analyze the relationships between species and environmental influences. The results indicated that S.bedoti was significantly correlated with temperature, the density of copepods and the density of phytoplankton. And S. enflata was significantly correlated with temperature, the density of copepods, water depth and salinity. The null model was used to test the coexistence pattern between S.bedoti and S. enflata. It showed that the observed Pianka indexes have no significant difference with simulated values between S.bedoti and S. enflata communities. It was suggested that there was a random distribution between S.bedoti and S. enflata communities, and competition and habitat filtering effects restricted their distribution. In addition, ecological niche differentiation of S.bedoti and S. enflata happened occurred in both time and space. Whether there was difference in food composition still needs further study.