Abstract: In order to study the relationship between herbaceous plant diversity and canopy structure in urban forest, this paper investigated the structure of herbaceous plants in a 1 hm^2 plot of Chongming Island in Shanghai. The results showed that: (1) There were 40 species of herbs in the plot which belonged to 20 families and 39 genera, and the species of Asteraceae family were dominant. (2) The understory herbaceous structures, the dominant herbaceous species and their species diversity indexes in different communities were significantly different. The diversity index of herbaceous plants in Cinnamomum camphora community was the largest, while that of Bischofia polycarpa community was the lowest. All indexes changed with the same trend, i.e., evergreen broadleaved forest (dominated by Cinnamomum camphora) > deciduous coniferous and broadleaved mixed forest (dominated by Metasequoia glyptostroboides-Bischofia polycarpa) > deciduous broad-leaved forest (dominated by Firmiana platanifolia) > deciduous broad-leaved forest (dominated by Bischofia polycarpa). (3) In the same community, the herb diversity indexes also showed a trend of an initial increase and then a drop with different gradients of density and canopy closure.