Abstract: Carex lasiocarpa is a rhizomatous clonal species of mire wetland in Northeastern China. The field studies about physical process of Carex lasiocarpa wetland was carried out in the Shangjiang Plain Mire Wetlands Ecological Experiment Station(47°31′N, 133°31′E)of the Chinese Academy of Sciences. The sampling area is 200×450m2 and was divided into three areas including the determined area of biomass, the determined area of wither biomass and the decompose area. Samples were taken 30 days once during May and October in 1998 and 1999. Sampling area was 1×1m2 and 2 to 3 replicates for each. The plants were divided into different components including leaf, sheath, rhizome,inflorescence, spike,radicula and dead standing. All samples were ground into pieces and dried to constant weight at 80℃ for analysis. The energy content is determined by bomb carlorimeter(Parr, USA). The photosynthesis is determined by photosynthesis meter(CID company, USA)The results showed that the net photosynthesis rate of Carex lasiocarpa(47.41 μ mol/m/s)is faster than those of other plants in Carex lasiocarpa wetland, Based on the overall sunlight radiation and the efficient photosynthesis radiation, energy utilization rate in radicula was the highest(1.3945% and 3.1879%)While those in spike was the lowest(0.0020% and 0.0046%). Energy utilization efficiency of Carex lasiocarpa population is 2.54%. The average energy content of underground components of Carex lasiocarpa community is bigger than those in other community. It showed that C. lasiocarpa had higher energy productive efficiency and most energy was stored in their underground part. Energy contents in underground components decreased with the increase in depth in soil.