The limited site conditions of waterfront green space restrict the use of plants. Studying the plant diversity of waterfront green space and exploring the impact of plant diversity on plant landscape can help urban waterfront green space give consideration to plant landscape design and ecological benefits. This paper selects Xuhui Riverside, a representative waterfront green space in Shanghai, as an example to investigate 14 sample plots. The plant diversity index of the sample plot was calculated, the SBE method was used for landscape evaluation, and the Spearman correlation was used to analyze the correlation between the two. The results showed that the plant diversity of Xuhui Riverside was low, and the species diversity of arbor was higher than that of shrub; Landscape evaluation is primarily positive; Landscape effect is positively correlated with vertical layers, total species, number of shrub species, total Simpson index, total richness, and shrub richness. Finally, some suggestions are put forward to improve the landscape and plant diversity of waterfront green space simultaneously: further, enrich the level of plant configuration and landscaping, increase the application of shrubs, and ensure the essential plant growth and maintenance.