Abstract: In order to study the effect of boron on sugar beet protective enzyme system and the correlation between protective enzyme system and endogenous hormones under different boron levels, and then enrich the physiological theory of sugar beet, sugar beet‘HI0099’was selected as experimental material. Under hydroponic condition, four nutrition concentrations of boron were set to determine the protective enzyme system of sugar beet leaves and endogenous hormones content. The results showed that, for the four varieties of sugar beet under different boron treatments, MDA content of leaves decreased and proline content increased as the plant growth. MDA content of leaves and proline increased under boron stress treatments. Under different boron treatments, SOD activity of sugar beet leaves and POD increased as plant growth. In the same date, different boron concentrations presented a trend of deficiency or the SOD activity increased under toxicity stress. Under boron stress condition, SOD activity and ZT content presented a significantly negative correlation (P＜0.05); SOD activity and GA3 presented a highly and significantly negative correlation (P＜0.01). In different dates, the variation rule of CAT activity among all the boron nutrition treatments was the same which firstly decreased and then increased. Comprehensive analysis showed that boron stress caused membrane lipid peroxidation. Sugar beet leaves defended boron toxicity by increasing protective enzyme activity; however, its defensive capability was limited. With the plant growing, the defensive capability of sugar beet on boron stress reached a critical value. The variation of protective enzyme activity was no longer significant. Sugar beet plant growth which was under boron stress condition was controlled by protective enzyme system and endogenous hormones.