Abstract: In this paper, a main cultivar of sugar beet (Beta Vulgaris L.), KWS0143, was used as materials to study the effects of nitrate nitrogen fertilization on nitrate reductase (NR) and nitrite reductase (NiR) activities, photosynthetic rate and total content of chlorophyll. There were four nitrogen levels (N 0, 60, 120 and 180 kg/ha). The relationships between nitrogen level, NR activity (NRA) and NiR activity (NiRA) were discussed. The results show that the dynamic change of photosynthesis rate is a single peak curve, while the changes of NRA, NiRA and total content of chlorophyll are double peak curves. The peaks of the changing curve of total content of chlorophyll are earlier than those of NRA, and the peaks of NRA are earlier than those of NiRA. The photosynthesis rate, total content of chlorophyll, NRA and NiRA are significantly increased under the nitrogen application amount of 120 kg/ha. Compared with 120 kg/ha, the photosynthesis rate and total content of cholorophyllre are not obviously changed under the nitrogen application amount of 180 kg/ha, while to some extent, NRA and NiRA are improved. In this experiment, sugar beet yield is increased with the increase of nitrogen level, while the rate of sugar content is decreased. The highest sugar yield is obtained under the nitrogen application amount of 120 kg/ha.