The effect of dike age on distribution of pill bug (Armadillidium vulgare Latreille, 1804) in the forests was studied at a reclaimed coast in Yancheng, China. The aggregated distribution of A. vulgare population was found by Taylor’s power law and Iowa’s patchiness regression methods in each season (P< 0.001). The abundances were markedly affected by habitat type (F5,120 = 49.409, P < 0.001) and season (F3,120 = 13.577, P < 0.001), however, there was no significant interaction of habitat type and season (F15,120 = 0.529, P = 0.919). The abundances distribution was significantly different among habitats in each season as shown by one-way ANOVA, the higher abundance can be found in the warmer seasons. The highest abundance of A. vulgare occurred in forests with dike age above 100 years in summer, whereas the lowest occurred in the forests with shortest dike age in spring. Pearson’s correlation coefficient analysis of individuals’ data indicated that there were significant correlations of abundances distribution among seasons (P < 0.050). The distribution of A. vulgare varied among different forests, and then the environmental change according to the dike age increasing should be considered as the main factor explaining such variation.