Spatial niches refer to the position occupied by a population in the ecosystem and its temporal and spatial interaction with other populations. It plays an important role in the study of the structure and function of species, biodiversity, interspecific relationships, community succession and population evolution. Based on two seasonal investigations conducted in spring and summer 2018 in the offshore waters of Yantai, the Levins formula and the Pianka index were used to study the niche breadth and niche overlap index of dominant zooplankton species. Redundancy analysis (RDA) was used to study the main environmental factors which influenced the differentiation of spatial niches of dominant zooplankton species. The results showed that planktonic larvae and copepods were dominant in the zooplankton community of offshore Yantai and that the dominant species replacement rate was 73.33% from spring to summer. The niche breadth values of dominant species (classes) of zooplankton could be classified into three groups: the broad niche group, the middle niche group and the narrow niche group. The broad niche group species were the main constituent of the dominant species (classes). Representative species of the broad niche group were Oithona brevicornis, Oithona similes, etc., in spring, and Paracalanus parvus, Acartia clause, etc., in summer. Additionally, we found that the niche overlap index was closely related to the spatial location of the species: the higher the value was, the more their habitats overlapped. Notably, the niche overlap index of the broad niche species was higher than the narrow ones. The main factors affecting the spatial niche differentiation of dominant zooplankton species (classes) were seawater temperature; salinity and DIN in spring; and salinity, Chl a, DIN and PO₄-P in summer.