Water temperature is an important factor affecting fish activities, and fish in stages such as breeding, growth, and development, have different demands in terms of water temperature. Based on survey data from four seasons in 2014 to 2015-using frequency and biomass approaches and the R language drawing technique-the water-temperature distribution characteristics of small yellow croaker () were analyzed and compared. The results show that the ranges of temperature distribution, determined using frequency and biomass, were obviously different, and the proportion of the former covers a relatively high proportion of survey stations, and the latter has a higher proportion of accumulated biomass. The latter is in the condition of ensuring a high biomass accumulation proportion, and can also have a higher proportion of station coverage in special seasons, such as summer and fall; based on the biomass to determine the temperature range can better reflect the distribution characteristics of target objects. Compared with the results of historical research, the water-temperature distribution range of this paper is basically consistent, and it is concluded that the water temperature distribution range of small yellow croaker is relatively stable. The results of this paper reflect the general characteristics of P. polyactis, and the distribution of temperature and space of the two groups was obviously different. One group was distributed northward, and the most southern distribution did not go beyond Zhoushan fishing ground; the other group was distributed southward, and the most northern distribution did not go beyond the Yangtze River-estuary fishing ground. The difference in the environmental characteristics of the population distributions can be used as a basis for population division. The results of this paper can be used as a side evidence for the division of . The results show that resource clustering in the spring and winter was higher than that in the summer and winter. The cold-season population structure was single, mainly the winter bait-chasing population, and the warm-season population structure complex, including spawning, recruitment, and other groups; the warm season appears multiple high biomass water temperature range, which may be related to different temperature preferences of the different groups.