Species coexistence is one of the core issues in community ecology, and exploring the coexistence patterns of community species can help with better understanding the ecological processes that affect community assembly. In the context of frequent El Niño-Southern Oscillation (ENSO) events, the changes in species coexistence patterns of fish communities and their responses to ENSO events in the bay remain largely unknown. Changes in species co-occurrence patterns within fish communities over the past decade and their relationships with the Oceanic Niño Index (ONI) were examined using null model analysis based on the data collected from the fish resources survey in the spring and autumn in the Haizhou Bay and its adjacent waters from 2013 to 2022. The results showed that the fish communities in the Haizhou Bay generally showed a nonrandom species co-occurrence pattern from 2013 to 2022, and exhibited an aggregation co-occurrence pattern in most years, with the aggregation pattern more pronounced in autumn than in spring. The species co-occurrence pattern of fish communities was influenced by important species pairs, and the important species pairs varied in different years. In most cases, dominant species such as Enedrias fangi and Hexagrammos otakii formed an aggregated coexistence pattern with other fish species, while fish species such as flatfish and Callionymus formed a segregated coexistence pattern with other fish species in most cases. The species co-occurrence pattern of fish communities was influenced by the selection of C-score and V-ratio indicators in the null model analysis. The fish communities were almost always in an aggregated co-occurrence pattern at ENSO neutral conditions. However, the species co-occurrence pattern mostly shifted from an aggregated pattern to a random pattern when ENSO events occurred, and there was a certain correlation between the fluctuation trend of ONI and species co-occurrence pattern of the fish communities.