In order to reveal the law of soil water and nitrogen transport and transformation under different fertilization timing (the whole process, the first 1/2 and the last 1/2 infiltration water fertilization), we analyzed the migration and transformation law of soil water and nitrogen distribution and redistribution under different fertilization timing, and compared their effects on soil nitrogen content quantitatively based on the one-dimensional vertical fertilizer solution (urea) infiltration experiment of sandy loam and clay soil. The results showed that fertilization timing hadlittle effect on the cumulative infiltration of soil and the distribution of water in moist body, but it had a significant effect on the transport and transformation of different forms of nitrogen in the process of distribution and redistribution. At the end of infiltration in sandy loam and clay loam, during the whole processand fertilization of the last 1/2 infiltration water, the content of urea nitrogen, ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) decreased with the increasing of soil depth. When the first half of the infiltration water was fertilized, the content of urea nitrogen and NO₃^--N accumulated at the edge of the wet body, andNH₄⁺-N increased first and then decreased, mainly distributed in 5-25 cm soil layer. In the redistribution stage, urea nitrogen in sandy loam and clay loam was basically hydrolyzed after 3 and 5 days of redistribution during the whole process and the last 1/2 infiltration water fertilization, respectively. At the same time, NH₄⁺-N content reached the peak, and NO₃^--N content did not decline within 10 days of redistribution. When the first half of the infiltration water was fertilized, the hydrolysis of urea nitrogen was basically completed after 10 days of redistribution, the content of NH₄⁺-N reached the peak after 5-10 days of redistribution, and the content of NO₃^--N increased first and then decreased. Under the condition of the last 1/2 infiltration water and the whole process of fertilization, when sandy loam and clay loam were distributed for another 10 days, the content of NH₄⁺-N and NO₃^--N in the 0-40 cm soil layer both were greater than those of the first 1/2 infiltration water, indicating that its potential nitrogen utilization efficiency was high. Therefore, it was recommended that the rational fertilization time of border (ditch) irrigation was the last half of the infiltration water or the whole process of fertilization. The results of this research could provide theoretical basis and technical support for the design and management of farmland border (ditch) irrigation and fertilization system.