When using the unique in terms of the volumes of databases on the level of a stand of Picea and Abies spp., the trans-Eurasian additive allometric models of biomass for Eurasian forests are developed for the first time, and thereby the combined problem of model additivity and generality is solved. The additive model of forest biomass of Picea and Abies is harmonized in three levels, one of which provides the principle of additivity of biomass components, the second one is associated with the introduction of dummy independent variables localizing model for eco-regions of Eurasia, and the third one makes the biomass structure of spruce and fir compatible by means of binary variable. The model can be developed further according to the third level of harmonization, when instead of the binary variable one can include another block of dummy variables coding the membership of actual biomass data of each eco-region to basic forest-forming wood species in Eurasia. This might be a subject for further research. © 2018 CEUR-WS. All rights reserved.