The study with pot experiment showed that under the stress of low soil moisture content, the oilseed rape cultivars with high and low boron (B) use efficiency had a higher fresh mass per plant at their seedling stage under high B supply, compared with those under low B supply. The increment was 43.1% and 31.7%, respectively, but no significant difference was observed between the cultivars. Under two B supply levels, the bound water content and semi-bound B distribution proportion in the leaves of the cultivar with high B use efficiency were 11.4% and 1.7%, and 6.9% and 23.8% higher than those of the cultivar with low B use efficiency, respectively. Under normal soil moisture condition, high B supply induced an increase of fresh mass per plant by 11.1% for the cultivar with high B use efficiency and by 27.4% for the cultivar with low B use efficiency, compared with low B supply. Under these two B supply levels, the cultivar with high B use efficiency had a higher content of free water in its leaves, and its leaf free B content was 2 times as much as that of the cultivar with low B use efficiency, which would benefit the B transportation in plant.