Abstract: By the methods of sampling typical plots and allometric dimension analysis,the underground and aboveground biomass and net primary productivity(NPP) of Populus×euramericana cv.San Martino'(I-72/58) plantation with different densities were measured on the beach land of Yangtze River in Anqing City,Anhui Province.The results showed that the biomass of the stand increased from 102.40 t·hm-2to 147.2 t·hm-2,the productivity increased from 7.31 t·hm-2·a-1 to 10.52 t·hm-2·a-1with the trees number increased from 250 to 370 per hectare.Aboveground and underground biomass accounted for 90% and 10% of the total biomass.In aboveground biomass, the stem,branch,bark and leaf account for 54%,28%,7% and 1%,respectively.The diameter class distribution of biomass and tree' numbers both took on irregular undee curve in plantations with four different densities;at the same time,the more the portion of high diameter class,the more the biomass of the Populus×euramericana cv.'San Martino(I-72/58)'forest in a plantation with same density.