Under the hydrological processes of soil matrix infiltration, the effect of fertilization measures of eucalyptus plantations during the short rotation period on groundwater needs a new understanding. The surface soil (0-20 cm) of differently aged eucalyptus plantations (1 year, 2 years, 3 years, and 5years) were used as the research object. Filled soil columns were used to simulate the leaching process of ammonium nitrogen, nitrate nitrogen, total dissolved nitrogen, and dissolved organic nitrogen driven by matrix infiltration. The change between the infiltration characteristic parameters and the leaching process of different forms of dissolved nitrogen and their influence factors were studied. Results showed that: (1) The steady infiltration rate and cumulative infiltration showed an increase-decrease-increase trend with plantation age increment, therein the steady infiltration rate (143 mm/h) and cumulative infiltration (279 mm) of on the suface soil of 2-years old eucalyptus plantation were the largest. (2) The concentrations of different forms of dissolved nitrogen in the leachate reached to the peaks at the beginning of leaching process and gradually decreased with the matrix infiltration rate decrease. Also, the matrix infiltration rates and the concentration of four nitrogen forms in the leachates showed the well linear relationships. (3) The nitrate nitrogen and dissolved organic nitrogen were the main forms of nitrogen leaching on the surface soil of eucalyptus plantations. The sand content increment promoted the nitrogen leaching, while the clay content and soil organic matters increment restrained the nitrogen leaching. Simultaneously, the concentrations of ammonium nitrogen at the initial leaching stage were higher than the threshold of groundwater quality, which was a potential threat causing the groundwater pollution in eucalyptus plantations. In summary, soil matrix infiltration was an important factor of nitrogen leaching of topsoil in eucalyptus plantations, and they had the coupling change trend and a linear relationship. The contents of sand, clay, and soil organic matters were the important factors affecting the nitrogen leaching on the surface soil of eucalyptus plantations.