A field experiment with two treatments, i.e. FI (flood irrigation) and BI (border irrigation), was designed and performed for the purpose of exploring a more effective irrigation mode based on traditional mode. The study was conducted to determine the effect of different irrigation modes on soil water content, soil water potential and vertical distribution characteristics of poplar root system and nitrate transport pattern in 0-100 cm soil layer. Results showed that BI decreased the soil water content and water potential in 0-40 and 60-100 cm layers with increased soil depth, indicating the weakened water deep seepage in the BI treatment. Root biomass decreased along with increased soil depth. Additionally, most of the roots concentrated in the 0-40 cm soil layer. Compared with the FI treatment, the BI treatment decreased root biomass in the 0-20 cm soil layer by 8.28%, whereas that in the 20-80 cm increased by 35.87%. Besides, the BI treatment increased the total root biomass in 0-80 cm soil layer by 5.52%, resulting in a higher extinction coefficient (β). As a result from BI, additionally, the nitrate content in 0-40 cm soil layer significantly increased, whereas that in 60-100 cm significantly decreased. Hence, border irrigation benefited the poplar root distribution. In conclusion, the BI treatment encouraged reasonable poplar root distribution, benefited water and nutrient absorption, and reduced nitrate leaching, which are important for the increased fertilizer use efficiency, environment protection and potential productivity of poplar.