Abstract: Understanding mechanisms structuring coexistence of species within biological communities is a central issue of community ecology. It is widely recognized that structure of fish community is mainly regulated by abiotic factors (e.g., salinity, temperature), as well as most of fish species co-occurred temporally in estuaries, e.g., spawning and nursing mainly during spring and summer. Thus, we hypothesize that environmental filtering is an important force promoting the coexistence of fish species in those environments. Aiming to examine such hypothesis, we analyzed the temporal niche overlaps among fish species within assemblages using null models, and relationships based on GAMs between fish species and abiotic factors of Changjiang Estuary. Results of null models and GAMs are as follows. Firstly, observed values of niche overlaps are more than expected ones. Secondly, fish assemblages were expressed well by abiotic variables, which together suggesting that environmental filtering mechanism plays a critical role but other unmeasured influences (e.g., inter-specific competitions) may also promote temporal distribution of fish species. Thus, the present study supports the theory of environmental filtering.