Abstract: The earliest nitrogen cycle on the earth was controlled by both atmospheric reactions and geological processes. Approximately 2.7 billion years ago, a linked suite of microbial processes evolved to be the most crucial driving force to control the nitrogen transformation, resulting in the current modern nitrogen cycling model. There is a different isotope effect associated with different microbial metabolism and this signal of isotope fractionation is reserved in the palaeobios. Therefore, nitrogen biogeochemical cycle in ancient oceans could be reconstructed by analyzing the stable isotopic ratio of nitrogen in the palaeobios.