Abstract: In order to find the correlation between assimilation product distribution in alfalfa organs and its tolerance to Odontothrips loti, the resistance, growth characters and soluble sugar in roots, stems and leaves were evaluated under different O. loti densities, using resistant clone (R-1) and susceptible clone (I-1) as indicating materials. The results showed that the damage index of R-1 and I-1 increased with increasing thrips density, and the damage index of R-1 was significantly (P<0.05) lower than that of I-1 under the same thrips density. For both R-1 and I-1, the plant height, leaf area, stem diameter and internode length decreased after O. loti damaged, meanwhile the internode number, the diameter of collar root and main root and lateral root number increased. Under the low pest density, the aboveground biomass of R-1 and I-1 clones increased with the increasing pest density, but the root to shoot ratio decreased. Under the high pest density, the aboveground biomass decreased with the increasing pest density, but the root to shoot ratio increased. The curve inflection points between the root to shoot ratio and pest density, and between the stem biomass and pest density were 5 thrips adult per branch for R-1 clone, and 3 thrips adult per branch for I-1 clone. For R-1, under the low pest density, the soluble sugar content in stems and leaves increased with the increasing pest density. Under high pest density, the soluble sugar content in stems and leaves decreased with the increasing pest density. The soluble sugar content in roots of R-1, and in stems, leaves and roots of I-1 decreased with the increasing pest density. In conclusion, the agronomic traits, resistance and utilization of assimilation distribution of R-1 alfalfa were higher than those of I-1 alfalfa.