In order to evaluate effects of crop straw biochar on soil productivity and C sequestration in paddy soil of the Tai Lake plain, the rice/wheat crop growth, nutrient uptake by crop plants as well as soil physicochemical characteristics were investigated after the successive incorporation of biochar from rice straw into a rice-wheat rotated soil during a 2-year (four rice/wheat rotation seasons) pot experiment. The application rates of biochar were set as 0(as control; CK), 4.5and 9.0t/hm², respectively. Each treatment was replicated in three pots. Each pot was kept the same dosage of NPK fertilizers, the same application methods as well as the similar water management. Before crop season, the biochar (passed through a 2cm sieve) homogeneously was mixed with 0-10cm soil in pots. The results showed that w(soil total organic carbon, TOC) and w(soil total nitrogen, TN) increased with increasing biochar application. TOC and TN increased by 46.7%-113.0% and 9.3%-28.3% at 9.0t/hm^2biochar application rate in the four crop seasons, respectively. Biochar application increased the above-ground biomass of rice/wheat (grain yield increased by 11.4%-60.5%, straw yield increased by 15.0%-56.8%) as well as enhanced the accumulations of N, P, K, Mg and Ca. Accordingly, the amount of total nitrogen in the soil increased after biochar application, as well as soil available nutrients (Mehlich Ⅲ extraction) such as w(available P)、w(available K)、w(available Mg)and w(available Ca). In addition, values of pH and cation exchangeable cations (CEC) increased, while soil bulk density decreased. The results demonstrated that the successive application of biochar produced from crop straw could sequester C, enhance C storage capacity as well as ameliorate soil properties, improve soil fertility and enhance crop productivity in rice/wheat paddy soil of the Taihu Lake region.