Viral attachment to specific host receptors is the first step in viral infection and serves an essential function in the selection of target cells. In this study, structure analysis, neutralization assays, and cell attachment assays were carried out to evaluate the cell attachment functions of the outer capsid fiber protein of grass carp reovirus GD108 strain (GCRV-GD108). The GCRV-GD108 fiber protein contained 512 amino acids encoded by S7 segment and shared sequence similarities with mammalian reovirus cell attachment protein σ1 and adenovirus fiber. Structural analyses predicted the presence of a coiled-coil tail domain, three adenoviral shafts in the body domain, and a globular head domain, similar to other fiber proteins. Neutralization assays showed that polyclonal antibodies against the fiber protein could prevent viral infection in both fish and grass carp snout fibroblast cells (PSF), suggesting that the recombinant fiber protein could induce neutralized antibodies against GCRV-GD108. Cell attachment assays showed that recombinant fiber protein could bind to PSF cells, demonstrating that the fiber protein functioned as the cell attachment protein in GCRV-GD108. These results provided the basis for further studies of the pathogenesis of grass carp reovirus.