Data of LAI(Leaf Area Index) are needed to study characteristics of photosynthesis and evaporation by canopy of plant community. The indirect method—Imaging Digital Canopy, based on “gap-fraction” process, was described in this paper. By study in various communities about 9 measuring spots, it showed characteristics of community such as LAI, radiation transmission, extinction coefficient. LAI of Vatica hainanensis forest was measured according to height of community in different developing stage. The technique to minimize error about the Digital Plant Canopy Imager CI110 was mentioned. It was discussed that LAI of Vatica hainanensis forest was lower than that of typical rainforest. It also certified that LAI of seashore rain forest was lower than that of typical mountain rainforest. And LAI correlation of various vegetations was also mentioned. The result should supply scientific basis to study on air environmental effects of tropical seashore vegetation, especially in O2/CO2exchange, water recycle and water-lose, solar energy utilization efficiency.