In order to evaluate nitrogen loss with runoff from paddy field and its affecting factors in the rice season,field experiments were carried out for three years in succession in the Taihu Lake region.When heavy rain shower brought water table of the flooded water 7 cm above the land overflow was piped to a runoff pooling pond.Results of the experiments show that dissolved N (DN) was the main form of N lost with runoff.Among the DN concentration of NH₄⁺-N was lower than that of NO₃^--N in general,and the former was correlated with N fertilization rate but the latter was not.Seasonal TN loads in runoff ranged between 1.0 and 17.9 kg hm^-2 during the rice seasons,accounting for 0.3%～5.8% of the applied N.N loss with runoff differed greatly between rice seasons and increased with the N rate in the same rice season.The relationship between TN loads in runoff and N concentrations in surface water before runoff could be expressed by equation y=ax+b.The risk of N losses through runoff in the rice season could be minimized by reducing fertilization rate,avoiding fertilization just before heavy rainfall and heightening the ridges of the paddy field.