Community assembly was a core issue in ecological research. Studying community assembly of wetland plants would be important for the restoration and reconstruction of wetland plants. Using the Fuzhou section of the Minjiang River as a research object to investigate the main driving forces of plant community assembly in urban riverine wetlands. Based on the combination of phylogeny and functional traits, the aboveground and underground plant functional traits and soil environmental factors were measured at four typical urban riverine wetland parks in the study area, then the phylogenetic tree was constructed, the phylogenetic signals and the phylogenetic index were calculated. The results showed that: (1) In the four wetlands, there was significant variation in soil factors and plant functional traits, with the greatest variability in soil conductivity and specific root length. Soil water content and soil electrical conductivity were the main factors affecting the variation of plant traits. (2) Except for leaf total nitrogen content, there is no significant phylogenetic signal in the other functional traits, indicating that the functional traits showed trait convergence. (3) The phylogenetic structure of Ganzhe wetland and Wulong River wetland tended to diverge, and environmental filtering played a dominant role in plant community assembly. The phylogenetic structure of Tajiaozhou wetland and Minjiang River Estuary wetland showed aggregation, and limiting similarity was the main driving factor. As a result, the assembly process of the plant community in the wetland of Fuzhou section of the Minjiang River was dominated by niche theory. The environmental filtering and the limiting similarity are the main driving factors. Soil water content was the main constraint to plant species coexistence. Variability in environmental factors influenced the drivers of ecological niche differentiation. Interspecific and intraspecific variation in plant functional traits reflected species responses to environmental change.