Carbon accumulation and distribution were studied in plantation of Pinus massoniana and Cunninghamia lanceolata mixed forest ecosystem in Daqingshan,Guangxi.The results shew that the mean carbon concentrations of two trees species was different, the total carbon concentrations of Pinus massoniana was much more than that of Cunninghamia lanceolata.The average carbon concentrations in all organs of Pinus massoniana was in the following order:wood(58.6%)>root(56.3%)>branch(51.2%)>bark(49.8%)>leaf(46.8%),the order of Cunninghamia lanceolata was bark(52.2%)>leaf(51.8%)>wood(50.2%)>root(47.5%)>branch(46.7%).The carbon concentrations of soil (to 60cm) ranged from 1.45% to 1.84%,with an average of 1.70%.Carbon concentrations of surface soil(to 20cm) was higher than the other layer. The average carbon concentrations in different layers was in the order as: trees (51.1%)>standing litters(48.3%)>shrub (44.1%)>herb (33.0%). The biomass of trees in three plots ranged from 85.35 t•hm^－２ to 101.35 t•hm^－２,with average of 93.83 t•hm^－２,which was contributed mainly by Pinus massoniana (75.7%～82.6%). The biomass of understory plant was 2.10～3.95 t•hm^－２, with an average of 2.72 t•hm^－２. Standing stock of ground litter was 5.49～7.91 t•hm^－２,with an average of 6.75 t•hm－２.The carbon storage order of mixed forest ecosystem was soil layer>vegetation >standing litter. Of total average carbon, 29.03% was distributed by vegetation component,69.02% by soil (60cm depth),only 1.82% by standing ground litter layer. The carbon storage of tree layer occupied 23.90% of total ecosystem and 97.7% of vegetation layer. Of total carbon storage in tree layer,65.39% was distributed by Pinus massoniana. The carbon storage in different organs was positively related to the biomass of corresponding organs. Trunk accumulated the highest carbon storage, comprising 53.23% of carbon storage in overstorey trees of Pinus massoniana, respectively seized 55.57% of Cunninghamia lanceolata. Root made up 19.22% of total tree carbon. The annual net productivity of mixed forest plantation was 11.46 t•hm^－２•a^－１,stored carbon up to 5.96 t•hm^－２•a^－１,amounted CO_２ to 21.88 t•hm^－２•a^－１. Forest was a important sink of atmospheric CO_２.