Because of special physiochemical properties, biochar can be applied in farmland to improve soil fertility and quality and to promote the growth of crops, so it has become a study hotspot in the field of agricultural emission reduction and biological nitrogen geochemical cycle in soil microecosystem. As the extraneous material of soil, biochar is directly or indirectly involved in the process of soil nitrogen turnover, thus has an long-term impact on the existence and supply capacity of nitrogen in soil. This paper analyzed the change and response mechanism of nitrogen turnover after biochar being fertilized in soil with emphases on biochemical reaction processes, such as ammonification, nitrification, denitrification and nitrogen fixation driven by microorganism after soil physiochemical changes caused by biochar application. Meanwhile, the study prospects of biochar were also discussed.