The shrub layer is a very important component in the warm temperate forest ecosystem. Accurate and convenient estimation of shrub layer biomass is a key point in the studies of forest biomass, circulation of materials and energy flow of the whole forest ecosystem. Allometric model can serve as a good method to achieve this goal. Studies on this subject have been employed around the world, but few studies have been taken in warm temperate forest in China. Aiming at this point, an investigation on forest understory shrub allometric modeling was established during growing season in 2011 in the region of Hebei Wulingshan Natural Reserve, which has the most typical Warm Temperate forest ecosystem, in North China. Basing on research data of this investigation, biomass allometric models for 15 common shrub species are constructed. The 15 shrub species include: Deutzia grandiflora, Syringa reticulata var. mandshurica, Campylotropis macrocarpa, Rhododendron mucronulatum, Weigela florida, Corylus mandshurica, Zabelia biflora, Rhododendron micranthum, Spiraea trilobata, Hydrangea bretschneideri, Rhamnus bungeana, Philadelphus incanus, Berberis amurensis, Rosa davurica and Radix Acanthopanais. The models of W=a(D²H)^b, W=a+bln(D²H) and W=a+bD²H+c(D²H)² were employed for the selecting of the optimal allometric equation to the 15 shrub species. The research result shows that D²H (where D means basal diameter and H stands for plant height) is the optimal variable of all the biomass allometric models of single organ or total plant. Power function of W=a(D²H)^b or quadratic function of W=a+bD²H+c (D²H)² is selected as optimal allometric equation to the 15 shrub species separately. Statistic results show that R² values are between 0.7331 and 0.9992 and P values are less than 0.01, which mean that the selected optimal equations are applicable to the biomass estimation of the shrub species in our study region. For more convenient application for the shrub biomass estimation in the warm temperate forest in North China, we classified and compared the allometric models of the total 15 shrub species to get a universal model for most of the normal shrubs in this region. The study of total plant biomass universal regression model shows that the quadratic function of W_TU=0.0362+297.03D²H-127.1(D²H)², (R²=0.9434 and P < 0.01) is applicable to 13 shrub species except for Zabelia biflora and Rhododendron micranthum among the 15 species. Further research is still required to explain why this model is not applicable to the rest 2 species.