Based on long term stationary experiment,effects of long-term nitrogen application on yield,carbon-nitrogen assimilation of leaves and soil nitrogen in permeable paddy soil in the Tai Lake region were studied Results show that no significant difference was found between the treatment applied with N 161.0 kg hm^-2and treatments applied with more nitrogen than N 161.0 kg hm^-2 in either yield or in carbon-nitrogen assimilation rate in leaves at the jointing,booting and filling stages.But all these treatments were higher than the treatments applied with N 57.5 kg hm^-2 in both indices.Analysis of nitrogen distribution in soil profiles reveals that soil N residue went down the deepest in the treatment applied with organic manure plus NPK,which was followed by treatments applied with N 161.0 kg hm^-2 or more in chemical fertilizer.And N residue was found the shallowest in the treatment of incorporation of crop stalks into the soil plus N application.