In the study of fish biology, stomach content analysis is the most common and important method to evaluate the feeding habits of fish species. In a fishery independent survey, stomach samples were generally collected randomly at different stations. The feeding habits of a predator within a certain area were estimated by calculating the arithmetic mean value of the predator’s diet information from different stations. This method is simple but ignores the spatial variation of the predator. Based on a fishery resources survey in the offshore waters of southern Zhejiang, a total of 750 stomach samples from Bombay ducks (Harpadon nehereus) were collected from March to November, 2019. Combined with the catch per unit effort (CPUE) difference in H. nehereus at different stations, the diet composition, feeding intensity, seasonal variation, and ontogenetic shift of H. nehereus were examined. Since each haul provided us with a group or “cluster” of H. nehereus for a given station, as in a cluster sampling design, this study introduces “cluster sampling estimators” to calculate the feeding habits of H. nehereus. The results showed that the prey items of H. nehereus included 11 prey categories and more than 40 prey species, with the index of relative importance percentage indicating that fishes (IRI%=82.29%) and shrimps (IRI%= 15.77%) were the dominant prey categories. Other categories included cephalopods, crabs, euphausiids, stomatopods, amphipods, etc. The dominant prey species were Benthosema pterotum, Apogon lineantus, H. nehereus, and Acetes chinensis. The main prey items were similar to those found in previous studies from the Yangtze River estuary, Yellow Sea, and other areas in the East China Sea; however, the dominant prey species varied in different sea areas. Obvious seasonal variations were indicated for the feeding habits of H. nehereus in this study: whereas fish were the most important prey group in all seasons, with higher than 85% for IRI% in spring and autumn, the proportion of shrimp consumed by H. nehereus in summer and winter was higher than that in other seasons. The seasonal variation in prey abundance among habitats is one of the main reasons for the seasonal variation in fish feeding habits. The feeding intensity of H. nehereus was higher in spring and autumn and the lowest in winter. The ontogenetic shift of H. nehereus was revealed in this study. With the increase in the body length of H. nehereus, its main prey items transitioned from small-sized items (such as small shrimp) to large-sized items (such as fish). This feeding characteristic is in accordance with the “optimal foraging theory.” With the development of feeding organs, the predation ability of H. nehereus is greatly enhanced, with the phenomenon of cannibalism mainly occurring in the larger group.