Abstract: With the switchgrass strains (Xiji No.1, Xiji No.2, Xiji No.3) as the dominated factors, the concentration of Agrobacterium tumefaciens as the deputy factors, the effect of switchgrass seed germination and seedling physio-biochemical characteristics were studied, using A. tumefaciens-soaking method. The results showed that the interaction effect between the strains and the concentration was not significant; The effects of A. tumefaciens on switchgrass strains were different, and the Xiji No.3 was more insensitive to A. tumefaciens than the other strains. With the concentration of A. tumefaciens increased, the switchgrass seed germination rate, the seedling plantingpercent and chlorophyll content showed downtrend, and the seedling POD activity, CAT activity and MDA content showed uptrend, and the seedling SOD activity initially increased but then decreased. To sum up, the most appropiate concentration of A. tumefaciens may be under 1.2 OD₆₀₀ in switchgrass seeds soaking.