Abstract:The distribution area of Larix gmelinii in the Da Xingan Mountain,Inner Mongolia, was divided into three zones. They are Southeastern Zone, Central Zone and Northern Zone, respectively. The biomass and net primary productivity of the natural young-and middle-aged stands of Larix gmelinii in the three zones were studied, based on the analysis of biomass from 237 sample trees, allometric dimension analysis of 814 trees, and field investigations conducted in 355 plots.An allometric model, lnW=lna+blnD + cD or lnW=lna + blnD2H +cD2H, which incorporates a variable allometric ratio (VAR), was used to fit to the biomass data of the bolewood, bolebark, live branch and leaf components of Larix gmelinii. Residual analysis showed that the VAR model significantly improved the estimation of live branch, leaf and bolebark biomass, and it provided less biased estimates compared with the CAR model, lnW=lna+blnD or lnW=lna+blnD2H. The VAR model is superior to the CAR model, particularly when the allometric relationships change in a linear fashion with increasing stem sizes.The aboveground biomass and net primary productivity of the stands were respectively 85.37 t·ha-1 and 9.86 t·ha-1·a-1 for young-aged group at the Southeastern Zone; 56.74 t·ha-1 and 7.29 t·ha-1·a-1 for young-aged group,72.34 t·ha-1 and 6.26 t·ha-1·a-1 for middle-aged group at the Central Zone; and 41.81 t·ha-1 and 5.29 t·ha·a-1 for young-aged group, 55.62 t·ha-1 and 5.02 t·ha-1·a-1 for middle-aged group at the Northern Zone. These data showed that the biomass and net primary productivity of the stands tended to decrease from the Southeastern Zone to the Northern Zone, or Southeastern Zone>Central Zone>Northern Zone.The reference ranges of the suitable density and leaf area index for stands of different zones were also given in this paper.