Four patches of poplar forest with different dike histories (about 30 to 200 years) were selected from the coastal area of Yancheng, China, for detecting the effect of dike age on soil macrofauna. A total of 825 individuals belonging to 21 taxonomic groups were collected. Omnivorous, phytophagous, predaceous, and saprophagous groups were classified on the basis of diet. Higher biodiversity values were observed in the forests with longer dike histories (100 and 200 years) than in those with shorter dike histories (30 and 50 years). By principal coordinate analysis, the soil macrofaunal communities from the forests were distinguished as three groups with shorter or longer dike histories (30 years, 50 years, and above 100 years). One-way ANOSIM analysis revealed significant differences among soil macrofaunal communities (P < 0.050), except for those with longer dike histories (100 and 200 years, P = 0.217). The groups of omnivorous and predaceous macrofauna showed no significant differences in taxonomic richness and abundance among habitats, while significant differences were observed between the other functional groups. A significant difference in functional composition between the soil macrofaunal communities in the forests with dike ages of 30 and 100 years was found with the chi-square test (P = 0.027). The biodiversity and functional composition of soil macrofauna was significantly affected by dike age in the reclaimed coast.