The invention relates to a field returning crop straw nitrogen fate quantitative measurement method and belongs to the farmland nutrient cycling technology field. The method comprises steps that a first experiment plot and a second experiment plot isolated from external soil are preset, crops are grown on the first experiment plot, highly abundant 15N-labeled nitrogen fertilizer is applied at a crop growth period, the crops absorb the nitrogen fertilizer, straw marking is carried out after harvest, the marked straw is moved to the second experiment plot for field returning, later crops are then grown, 15N contents left in the marked straw, absorbed by the later crops and contained in the soil are measured at a critical growth period and after harvest, and dynamic field returning crop straw nitrogen conditions and fate thereof can be quantitatively monitored. The method is advantaged in that a measurement result can relatively visually reflect the nitrogen fate, the method is stable and reliable, external factor interference can be avoided, and technical supports are provided for understanding and researching field returning crop straw nitrogen release, mineralization characteristics and crop utilization characteristics.