A trial of investigating impacts of nitrogen dressing at different stage on feeding value and physiological characteristics of forage summer maize (Ludan50) has been conducted by means of potted planting. The results suggested that biomass yield, grains yield and feeding value of all treatments were significantly raised compared CK without nitrogen dressing. Nitrogen dressing at the jointing stage for one time could raise the dry matter yield in terms of biomass, thus improving feeding value. Separating total dose of dressing nitrogen into two or three times at the jointing, male tetrad (or flowering) stage were beneficial to the dual purpose of maize, i.e. both kernel and forage. The effects on physiological characters were reflected as the improvement of leaf area index (LAI), activity of nitrate reductase (NR), catalase (CAT), superoxide dismutase (SOD), peroxidase (POD)and soluble protein content in leave above ear. Such impacts were more obvious at the late stage of maize growth.