The influence of long-term application of fertilizers and tillage of 12-year rice-based cropping system on soil nitrogen fertility was under conditions studied on Taihu region of the south Jiangsu Province. The results showed that total N content in the soil layer of 0-5 cm reached 2.89%(M) in the long-term fallowed soil. The treatment of fallow in combination with plowing every crop season reduced total N content to 2%, occupying 70% of the M value. The total N content accounted for 50% of M value for the treatment without fertilizer, 52%-56% for chemical fertilizer treatment only, 63% for treatment of pig manure plus chemical fertilizer and 63%-70% for crop straw-chemical fertilizer treatment. The various tillage methods significantly affected contents and distribution of soil total mineralization potential of N, microbial biomass N and mineral N in the soil profile. As to soil total N content and N supply capacity, fertilization, especially the combination of chemical fertilizer and organic manure played a greater role than the tillage did. The content of mineral-fixed ammonium in soil was related not only to soil clay minerals but also to fertilization.