Abstract: Under the field condition, effect of N application rates ( 0, 90, 180, 270，360 kg/ha) on fiber root growth, distribution and activity in sugar beet (Beta Vulgaris L) was studied. The aim of this experiment is to find the pattern of growth fiber root so as to provide scientific suggestions on rational fertilization in sugar beet. The results indicated that the increasing application rate of nitrogen significantly increased the numbers of lateral root from the superficial layer, fiber root dry weigh from deep and outer layer, and total fiber root dry weight in 100cm layer. It could also increase lateral root and taproot activity in the superficial layer at different growth stages. Compared with N0, application of nitrogen fertilizer increased the fiber root weigh of 100 cm soil layers by 60.4%~168.4%, the numbers of lateral root by 22.7%~75.1%, the fiber root of 0-20 cm and 40-60 cm layers and 80-100 cm deep and outer layer by 129.6%~266.8%, 71.0%~234.0%, and 101.5%~202.8%, and the bleeding quantity in top root of sugar beet in 25th. August and vigor of lateral root of sugar beet in 25th July by 56.2%~89.9%、23.7%~63.4%, respectively. Among the different treatments, N180 had the highest total amount of fiber roots within 100 cm soil layer, biggest root numbers in different soil layers, and the highest activity of taproot and lateral root at different growth stages. It had also the highest that sugar beet root yield (82609.63 kg/ha) and yield amount of sugar (13892.64 kg/ha), but lower sugar content (16.83%) compared to treatment N0 (18.341%). Rational N application resulted in deeper and more widespread fiber root, more root numbers, and higher activity of sugar beet root. It could also increase the yield of sugar beet root and sugar output.