Effect of fertilization on crop productivity and C cycling of cropland soils has been one of the foci in research of C cycling and global change. Taking an example of a long-term fertilization trial in a Ferric-accumlic Stagnic Anthrosols from the Tai Lake region, China, the effect of different fertilization treatments on crop C assimilation as indicated by grain yield and soil C sequestration was studied in this paper. The fertilization treatments studied were: no fertilizer application(NF), chemical fertilizers only(CF), combined fertilization of chemical fertilizers and straw return(CFS) and pig manure(CFM), respectively. The treatment plots were arranged in random block design in triplicates. The trials had been performed with rotation of rice and rape under minimum tillage consistently since 1987. The yield of rice and rapeseed was measured every year. Whole soil profile was sampled by depth interval sampling procedure in 2004 and topsoil samples from 0～5cm and 5～15cm were collected in 2005 after rice harvest. Soil organic carbon (SOC) content of the samples was determined with the wet combustion method. Significant difference in mean rice yield was observed between the treatments but in rape. Higher and more stable yield of rice was found under CFM and CFS than under CF. Effect of fertilization on C content and storage of topsoil but of whole profile was recognized. There had been a prominent topsoil C sequestration at rates of 0.1～0.4t/(hm^２•a) under fertilization. The increase of topsoil SOC content and storage was in proportional to the mean annual crop yield as described by well correlations of SOC content and C sequestration rate with root biomass input and total OC input to the soil. This demonstrated a key role of enhanced biomass C input in C sequestration of the paddy. Moreover, effect of applied N both on rice C assimilation as indicated by grain yield and soil C sequestration turned stronger under combined fertilizations. This, in turn, evidenced a Win-Win effect of enhancing and stabilizing crop productivity and C sequestration and greenhouse gas mitigation as well by paddies. However, the difference in the above-mentioned N effect could be in association with the difference in C partitioning in soil-crop system and C source utilization by soil organisms, which deserved further study.