Abstract: To clarify the effect of mixed organic liquid fertilizer on root morphological characteristics of forage crops in agro- pastoral ecotone of northern Shaanxi, sweet sorghum was used as the material in the pot experiment. Treatments with different concentrations of bacteria mineral water (BMW) (i.e. B1, B2, B3 and B4) and Aidoora solutions (i.e. A1, A2 and A3) were set, and the root morphological characteristics in the seedling stage of sweet sorghum were determined. The results showed that, under most single liquid fertilizer or mixed liquid fertilizer treatments, the root biomass (RB ), root shoot ratio (RSR ), root volume (RV ), total root length (TRL ), root surface area (RSA ), root average diameter (RAD ), specific root length (SRL ) and root area (SRA ) was higher than that of CK, which indicated that BMW and Aidoora solutions were favorable to improving the root biomass accumulation and absorbing capacity of root. Positive linear relationships existed amongRB ,TRL andRSA , which indicated that the total root length or root surface area increased with root biomass rising. These results suggested that, compared with other BMW and Aidoora solutions, B3A2 and B3A3 were the most suitable mixed organic liquid fertilizers to improve the root biomass accumulation and morphology formation in the seedlings of sweet sorghum.