Abstract: An experimental study was conducted in an indoor soil tank to examine to nitrogen infiltration and movement through unsaturated soil in topsoil layer of riparian zone.The timing of seepage flow from the tank and the seepage sequence at different sampling points were monitored.The variation of nitrogen concentrations(e.g.,total nitrogen TN and ammonia NH₄⁺-N)was also observed.Results show that the vertical velocity of percolation water is larger than the horizontal one during infiltration into the unsaturated topsoil layer of riparian zone.In the process from dry-towet and wet-to-dry,the TN and NH₄⁺-N concentrations first has a sharp increase and then gradually decrease until reaching a stable state.This is true for every monitoring point.In addition,the nitrogen retention capacity in the topsoil layer of riparian zone is high under unsaturated conditions.Along the 1.08 m long slope and 11 hours after the experiment began,the TN and NH₄⁺-N、oncentrations at points 12cm below the surface reduce by 74.23% and 68.02%,respectively.