Abstract: To investigate the significance of functional diversity among fish species in the Yellow River estuary and its adjacent waters, we selected 13 functional traits encompassing feeding, locomotion, ecological adaptation, reproductive behavior, and population dynamics in this study. Data were obtained from bottom trawl surveys conducted in the Yellow River estuary and adjacent waters over seven sampling events in June, July, August, and October 2013, as well as February, April, and May 2014. Utilizing three functional diversity indices: the functional richness index (FRic), functional evenness index (FEve), and functional divergence index (FDiv), along with the community weighted mean index (CWM), we examined spatial and temporal variations in fish community functional diversity. The results showed that the main species were those fish with functional trait such as benthic, low trophic level, low growth coefficient, high resilience, small mouth or lower mouth, eel-shaped and lateral flatform, and short-distance migratory or sedentary warm fish living in seawater and brackish water in each month. Notable examples included Chaeturichthys stigmatias, Cynoglossus joyneri, and Thryssa kammalensis. The FRic peaked at 0.805 in June while reaching a minimum of 0.324 in February; FEve was the highest at 0.510 in May but the lowest at 0.240 in August; FDiv reached its maximum value of 0.95 in October compared to a minimum of 0.236 observed in April. Overall, the findings revealed that FRic was the highest within the Yellow River estuary and its outer regions, decreasing along the northern and southern estuarine sides, FEve increased eastward from the coast, and FDiv was generally high, with lower values in the estuary and northern waters, and higher values in the southern and eastern regions. The functional diversity of fish communities is significantly correlated with temperature, depth, and salinity. The temporal changes in functional traits and functional diversity exhibited in the Yellow River estuary and its adjacent waters may be attributed to fish migration patterns.