LAI (leaf area index LeafArea Index,) is the study of green plant atmosphere O2/CO2 exchange, water cycle and water loss, solar energy utilization efficiency and conversion of the important basic work. Through the gap ratio (gap-fraction)principle, LAI digital imaging indirect method are described systematically. Through the determination of the South China different typical wetland canopy 9 observation points, the leaf area index, extinction coefficient, radiation through the characteristic index coefficient of community canopy. And by measuring height LAI characteristics of different stages of secondary forest. The CI110 digital canopy imager (Digital Plant Canopy Imager CI110) method to reduce human error.Also discusses the reasons of south China typical single and mixed forest of mountain rain-forest in LAI than in LAI minor. And the canopy LAI of different types of comparative analysis. The results provide scientific basis for the study of atmospheric environment effect for Hainan coastal vegetation.