Abstract: Winter wheat-summer maize rotation planting, with two harvests per year, is the main cropping system in the North China Plain (NCP), and plays an important role in ensuring national food security. Clarifying quantitatively the crop nitrogen nutrient source in the system is of great significance to the efficient management of nutrient resources, the optimization of fertilization system and the reasonable regulation of crop nutrition status. As the stable isotope of nitrogen, ¹⁵N has been widely used in the field of agricultural production, such as the fates of nitrogen fertilizer applied to soil, the sources of crop nitrogen nutrition, and so on. The objective of this study was to summarize nitrogen nutrition contributions of chemical fertilizer-N applied in-season, residual fertilizer-N applied in the previous season, and soil inherent nitrate-N prior to sowing to winter wheat and summer maize in NCP using ¹⁵N isotope tracing technology. Meanwhile, some case studies and related research results were also introduced. Moreover, we put forward the prospect on the study on other nitrogen nutrient sources, such as foliar fertilizer nitrogen, nitrogen in straw returning to the field, atmospheric dry and wet deposition nitrogen etc. The study aimed to provide theoretical reference for optimizing nitrogen nutrient resource management and fertilizer-N application schedule in the wheat-maize double cropping system in NCP.