The woody shrub layer in the Tianshan Mountains comprises a large proportion of the plant biomass of the entire forest ecosystem, significantly affecting estimates of the total forest biomass. Therefore, using an average wood-harvesting method, this study measured both the aboveground and belowground biomasses of six species of dominant woody shrubs (Rosa spinosissima L., Berberis heteropoda Schrenk., Lonicera hispida Pall., Spiraea tianschanica Pojark, Juniperus pseudosabina Fisch. et Mey., and Cotoneaster melanocarpus Lodd.) in eastern, central, and western areas of the Tianshan Mountains. A series of individual biomass models inferred from the variable D²H were established. The results are as follows: (1) The total biomass of the forest in the western areas of the Tianshan Mountains was larger than that in the central and eastern areas. The average biomass of an individual plant of the six woody shrubs was in the order of Lonicera hispida > Cotoneaster melanocarpus > Berberis heteropoda > Juniperus pseudosabina > Spiraea tianschanica > Rosa spinosissima. (2) In the western areas of Tianshan Mountains, the ratio of aboveground biomass to belowground biomass was greater than 1 for all six species; in the central area, it was less than 1 for all species except R. spinosissima and L. hispida; and in the eastern area, it was less than 1 for all species except B. heteropoda. (3) In all species, roots and branches were the major contributors to the biomass. The plant organ biomass was in the order of root < branch < leaf. The biomass of different root sizes was in the order of thick root > large root > medium root > small root > fine root. The variation in biomass distribution among different nutritive organs and diameter-class roots reflects the strategies that species employed to adapt to selected habitats. (4) Twenty-four biomass estimation models, with D²H as an independent variable, were established to evaluate organ biomass and individual biomass in the six species. The established models included 10 linear models, eight power function models, four polynomial models, and two logarithmic models. Except for B. heteropoda and J. pseudosabina, which reached only the significant level, the biomass models for all species reached the extremely significant level. The results indicate that the models can provide highly accurate estimates that could be used to evaluate the biomass of woody shrubs. This study provides supporting data for quantitative assessment of carbon fixation capacity of the Tianshan Mountains forest ecosystem. In addition, it provides strong evidence for further evaluation of the service capacity of forest ecosystems.