Abstract: The Biomass,net primary productivity and dynamic changes of forest were determined and investigated on a thirty-five years old Podocarpus imbricatus plantation in Jianfengling,Hainan Island. The total biomass of tree layer of the plantation was 285.53 t·hm-2,of which the stem accounted for 190.82 t·hm-2,branches 35.93 t·hm-2,leaf material 7.96 t·hm-2 and roots 31.63 t·hm-2.Regarding the production structure,the biomass of trunk under the heights of 8 meters accounted for 80% of the total and which of the stumpage with the diameter class between 12 cm and 22 cm accounted for 70% of the total.The biomass of the plantation increased rapidly between 1 and 25 years and annual average net primary productivity increased with the age of the trees,but the growth slowed down after 25 years.It was a high productivity plantation with a net primary productivity averaged at 10.34 t·hm-2·a-1 and the highest one could reach as high as 13.99 t·hm-2·a-1.The integrate effects could be improved by regulating the present structure of the community.