On the basis of 16-year long-term located fertilizer experiments in paddy soil,the changes of four fertilization patterns(no nitrogen fertilizer,nitrogen fertilizer,organic fertilizer nitrogen fertilizer,organic fertilizer nitrogen fertilizer azolla) on soil mineralizable N and biomass N were studied by the short-term and long-term submerged incubation-intermittent leaching method and chloroform fumigated method.Results showed that after 16-year fertilization and planting of rice,the only nitrogen fertilizer application could decreased mineralizable N of paddy soil compared with no nitrogen fertilizer application(p<0.01),and combined application of farmyard manure and chemical nitrogen fertilizer could increase mineralizable N of paddy soil(p<0.01).The only nitrogen fertilizer and the combined application of farmyard manure and chemical nitrogen fertilizer application could increase the amount of biomass N in paddy soil(p<0.01),but the only nitrogen fertilizer application made a max increasing range.Based on combined application of farmyard manure and chemical nitrogen fertilizer,the soil mineralizable N and biaomass N were no obvious change compared with inoculating "Azolla" for 7-year after transplanting.There was no-linear positive correlation between soil mineralizable N and biomass N,but there was extremely significant linear positive correlation between soil mineralizable N and its ratio to biomass N.