Abstract: Amphipods play a crucial role in the marine ecosystem, serving as key conduits for transmitting energy from primary producers to the higher-level consumers. We conducted a systematic analysis based on the investigation data collected in the mussel-raft culture area near Gouqi Island, Zhejiang, the East China Sea, during August 2022 (summer) and February 2023 (winter). The analysis aimed to characterize the distribution of resource densities, spatial niche, and relationships with environmental factors for two amphipods species, namely Gammaridea and Caprellidae. The results showed that the average abundance of Gammaridea (6.65±3.17×10⁴) ind./m² was smaller than that of Caprellidae (27.51±21.50×10⁴) ind./m² in summer. Gammaridea predominantly inhabited the near-shore side, while Caprellidae were mainly distributed in the off-shore side of the culture area. The mass density of Gammaridea (69.07±37.13) g/m² was lower than that of Gammaridea (752.22±707.03) g/m². Both Gammaridea and Caprellidae exhibited increasing mass densities from the center to the periphery of the culture area, with the minimum resource density observed at GQ3. In winter, the average abundance of Gammaridea (0.24±0.17×10⁴) ind./m² was slightly larger than that of Caprellidae (0.02±0.04×10⁴) ind./m². Similar to summer, Gammaridea mainly inhabited the near-shore side, while Caprellidae mainly occupied the off-shore side, gradually shifting towards the middle of the culture area. The mass density of Gammaridea (10.92±13.07) g/m² exceeded that of Caprellidae (1.27±2.57) g/m². In contrast to summer, mass densities showed a decreasing trend from the middle to the periphery of the culture area in winter. The spatial niche widths ranged from 0.78 to 2.08, with Gammaridea having the highest niche width in summer (2.08) and Caprellidae the lowest in winter (0.78). Niche overlap values ranged from 0.37 to 0.72, with a higher overlap in summer (0.72) compared to winter (0.37), indicating a strong competitive relationship between Gammaridea and Caprellidae in summer. Correlation analysis between two amphipods species and environmental factors showed that temperature, pH, NH₄-N and NO₃-N were identified as the main factors influencing the distribution characteristics of the Gammaridea and Caprellidae. This study aims to provide reference materials for the development of a multi-trophic layer culture model in mussel-raft culture areas and the modernization of marine ranching.