Abstract: Green algal blooms have occurred along the coast of China for more than 10 years, resulting in tremendous economic loss due to the destruction of marine ecosystems and damage to ecological service functions. This research was conducted to explore the biodiversity of epizoans attached on the green tide algae, Ulva lactuca. In October 2018, Ulva lactuca was collected from the sea area near Gouqi island, Zhoushan, and DNA barcode technology was used to carry out species identification. The results showed that the epizoans were mainly divided into the Caprellidea and Gammaridea. Some samples could not be identified, so there was the possibility of the emergence of new species. The dominant species included Caprella scauroides and Ampithoe lacertosa, etc, and Ampithoe lacertosa was recorded in the offshore of China for the first time. On the basis of the above, we further discussed the important role played by amphipods in maintaining the stability of the ecosystem, and clarified that it will be of great application value to study the feeding preference of different Gammaridea species in different seasons, which provides a new idea for the prevention and control of green tide outbreaks.