Abstract: In order to study the effects of nitrogenous chemical fertilizer applied into paddy field on surface and ground water, a large scaled apparatus with simulated soil layers and ground water was erected for the experiment. Results show that even if urea was blended with bio mineral complex fertilizers and applied at a moderate or low rate, pretty high contents of organic nitrogen and N H ₃- N were detected in the surface water and solutions of the plow layer and the other layers at different depth, considerably polluting the groundwater, which lacks adequate replenishment. Since N O₃^- - N will not last long in paddy field, its pollution may be neglected.