Plant nitrogen uptake is an important process in the subground nitrogen cycle. Correct simulation of plant nitrogen uptake is critical in computer modeling for watershed management. The plant uptake of dissolve inorganic nitrogen from soil is generally associated with water uptake, though in a smaller rate. Soil moisture plays an important role in water and nitrogen uptake. The uptake increases with the increase of moisture from the wilting point to approximate the field capacity, which reduces soil nitrogen storage and nitrogen export potential in later periods. A further increase in soil moisture above the filed capacity, nitrogen export would begin. Then, increasing moisture reduces dissolved inorganic nitrogen concentration and damages root due to anaerobiosis, which consequently reduces nitrogen uptake and increases nitrogen export due to higher outflow. Soil moisture also influences significantly on microbial activities and the related immobilization and mineralization, and the pool of inorganic nitrogen. This talk will present computer simulations of soil moisture-related nitrogen uptake for two types of uptake simulations, the Michaelis-Menton saturation kinetics and the yield-based plant uptakes. The improvement of plant nitrogen uptake simulation, associated with the improvement of immobilization/mineralization simulation, provides a better tool of computer modeling for watershed management.